Screening methods using canine t2r receptors and pet food products and compositions identified using the same

ABSTRACT

The presently disclosed subject matter relates to methods of screening raw materials and pet food products to manufacture a palatable pet food product. The presently disclosed subject matter also relates to methods for identifying compounds that modulate the activity and/or expression of a bitter taste receptor.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. Provisional Application Ser. No. 62/197,983, filed on Jul. 28, 2015, which is incorporated in its entirety herein.

FIELD

The presently disclosed subject matter relates to the use of canine T2R bitter taste receptors (cT2Rs) for the identification of T2R modulators. The presently disclosed subject matter further relates to the use of canine T2R bitter taste receptors to screen raw materials for making pet food products, as well as screening finished pet food products, for the presence of T2R modulating compounds.

BACKGROUND

Taste profiles for edible compositions include basic tastes such as sweet, salt, bitter, sour, umami and kokumi. Taste profiles have also been described as including free fatty acid tastes. Chemical compounds that elicit these tastes are often referred to as tastants. Without being bound by theory, it is hypothesized that tastants are sensed by taste receptors in the mouth and throat which transmit signals to the brain where the tastants and resulting taste profiles are registered. Taste receptors include the T2R family of receptors, which comprise a G-protein coupled receptors (GPCR) family that detects compounds associated with bitter taste sensory perception.

Pet food manufacturers have a long-standing desire to provide pet food products that have high nutritional value. In addition, and with particular regard to cat and dog foods, pet food manufacturers desire a high degree of palatability so that pets can receive the full nutritional benefit from their food. Domestic animals are notoriously finicky in their food preferences, and often refuse to eat a pet food product that it has accepted over time or refuse to eat any more than a minimal amount of a pet food product. This phenomenon may be, in part, due to the subtle differences in the sensory profiles of the raw material, which can be perceived by the domestic animals because of their gustatory and olfactory systems. As a result, pet owners frequently change types and brands of pet food in order to maintain their pets in a healthy and contented condition.

While there have been recent advances in taste and flavor technologies, there remains a need for methods of screening raw materials that are used to make pet food product, and for screening finished pet food products, to ensure that the most palatable products and processes for making the pet food products are used. There also remains a need for compounds that can enhance or modify the palatability of pet food products by enhancing or modifying the taste, texture and/or flavor profiles of the pet food products. The enhancement or modification can be used to increase the intensity of a desirable attribute, to replace a desirable attribute that is not present or somehow lost in the pet food product, or to decrease the intensity of an undesirable attribute. In particular, it is desirable to decrease the presence or intensity of an undesirable bitter tastant in a pet food product. Similarly, there is a need to increase the acceptance of pet medications by enhancing or modifying the palatability of the medications.

The pet care industry is also concerned with developing taste deterrents that can effectively discourage a pet from chewing, licking, or ingesting things that are harmful to the health of the animal. While it is known that bitter taste can be effective to deter pets, there is a significant variation in pets' reactions to these bitter taste deterrents. Thus, there exists a need for compounds that effectively impart an undesirable bitter taste to harmful or toxic objects.

Therefore, there remains a need in the art for methods to screen raw pet food materials (e.g. new protein sources), as well as final pet food products, to provide palatable and nutritious pet food. There also remains a need to identify compounds that enhance, decrease, or otherwise modulate the palatability and/or bitter taste of pet food products, or objects, and for flavor compositions comprising these compounds.

SUMMARY OF THE INVENTION

The presently disclosed subject matter provides methods for identifying compounds that enhance, increase, decrease and/or modulate the activity and/or expression of a bitter taste receptor. In certain embodiments, the methods entail screening for compounds that modulate the bitter receptor activity and/or expression in a pet food product or medicine, or in raw materials used to make the pet food product or medicine. The presently disclosed subject matter also provides compounds that enhance, increase, decrease and/or modulate the activity and/or expression of a bitter taste receptor identified by said methods. In certain embodiments, the bitter taste receptor is a T2R receptor. In other embodiments, the bitter taste receptor is a canine T2R receptor.

In certain embodiments, the method for identifying compounds that enhance, increase, decrease and/or modulate the activity and/or expression of a bitter taste receptor comprises expressing a bitter taste receptor having a nucleotide sequence set forth in any one or more of SEQ ID NOs: 1-16, or a fragment or variant thereof, in a cell. The method can further comprise contacting the cell expressing the bitter taste receptor with a sample (e.g., pet food raw material, finished pet food, or a test compound) and determining the activity and/or expression of the bitter taste receptor in the presence of the sample as compared to the activity and/or expression of the receptor in the absence of the sample. In certain embodiments, the activity and/or expression of the bitter receptor is determined in the presence of the sample and a bitter receptor agonist.

In certain embodiments, a method for identifying compounds that enhance, increase, decrease and/or modulate the activity and/or expression of a bitter taste receptor comprises expressing a bitter taste receptor having an amino acid sequence set forth in any one or more of SEQ ID NOs: 17-32, or a fragment or variant thereof, in a cell. The method can further comprise contacting the cell expressing the bitter taste receptor with a sample (e.g., pet food raw material, finished pet food, or a test compound) and determining the activity and/or expression of the bitter taste receptor in the presence of the sample as compared to the activity and/or expression of the receptor in the absence of the sample. In certain embodiments, the activity and/or expression of the bitter receptor is determined in the presence of the sample and a bitter receptor agonist.

In certain embodiments, the present disclosure provides a method for identifying a composition that modulates the activity of a bitter taste receptor comprising (a) contacting a bitter taste receptor agonist with a bitter taste receptor, (b) determining the activity of the bitter taste receptor, (c) contacting a test agent with the bitter taste receptor, (d) determining the activity of the bitter taste receptor, and (e) selecting the test agent as the composition when the activity of (d) is greater than or less than the activity of (b).

In certain non-limiting embodiments, the methods for identifying a compound that modulates the activity of a bitter taste receptor described herein utilize cells expressing a bitter receptor that is native to the cells. Examples of such cells expressing a native bitter receptor include, for example but not limited to, dog and/or cat taste cells (e.g., primary taste receptor cells). In certain embodiments, the dog and/or cat taste cells expressing a bitter receptor are isolated from a dog and/or cat and cultured in vitro. In certain embodiments, the taste receptor cells can be immortalized, for example, such that the cells isolated from a dog and/or cat can be propagated in culture.

The present disclosure also provides for methods for identifying compounds that enhance, increase, decrease and/or modulate the activity and/or expression of a bitter taste receptor, wherein the assay is conducted using a cell-free assay, for example, wherein the bitter taste receptor is bound to or otherwise attached to a substrate.

The present disclosure also provides for methods for identifying compounds that enhance, increase, decrease and/or modulate the activity and/or expression of a bitter taste receptor, wherein the assay is conducted using an in silico model of the bitter taste receptor, for example, wherein the bitter taste receptor is modeled using a computer program and binding of the compound to the receptor is predicted through docking algorithms.

The presently disclosed subject matter further provides a method for making a palatable pet food product, wherein the raw materials used to generate the pet food product are screened to determine if they contain compounds that enhance, increase, decrease and/or modulate the activity and/or expression of a bitter taste receptor. In certain embodiments, the raw material is a novel protein source. In certain embodiments the raw material is a protein source that is not commonly consumed in the human food chain. In certain embodiments, a raw pet food product that comprises a compound that increases the activity and/or expression of a bitter taste receptor (for example, as compared to a bitter taste receptor not contacted with the raw material) is not selected for use in generating a finished pet food product. In other embodiments, a raw pet food material that does not increase the activity and/or expression of a bitter taste receptor (or that reduces the activity of a bitter taste receptor, for example, in the presence of a bitter receptor agonist) is selected for generating a finished pet food product.

The presently disclosed subject matter further provides a method for making a palatable pet food product, wherein the finished pet food product is screened to determine if it contains compounds that enhance, increase, decrease and/or modulate the activity and/or expression of a bitter taste receptor. In certain embodiments, the compounds are formed during the manufacturing process. In one embodiment, a finished pet food product that comprises a compound that increases the activity and/or expression of a bitter taste receptor (for example, as compared to a bitter taste receptor not contacted with the finished pet food product) is supplemented with one or more compounds that decrease the activity and/or expression of a bitter taste receptor (for example, an antagonist compound).

The presently disclosed subject matter further provides a method for making a palatable pet medicine product, wherein the finished pet medicine product is screened to determine if it contains compounds that enhance, increase, decrease and/or modulate the activity and/or expression of a bitter taste receptor. In certain embodiments, the compounds are formed during the manufacturing process. In one embodiment, a finished pet medicine product that comprises a compound that increases the activity and/or expression of a bitter taste receptor (for example, as compared to a bitter taste receptor not contacted with the finished pet medicine product) is supplemented with one or more compounds that decrease the activity and/or expression of a bitter taste receptor (for example, an antagonist compound).

The presently disclosed subject matter further provides flavor compositions that comprise a modulator of a bitter taste receptor, e.g., an agonist and/or an antagonist and/or an allosteric modulator and/or an inverse agonist, identified according to the methods described herein.

In certain embodiments, said compounds can be used in methods for maintaining the health of an animal by imparting a bitter taste and/or decreasing the palatability of an object or surface. In certain embodiments, the method comprises applying a taste deterrent product comprising a compound as described herein to the object or surface. In certain embodiments, the object is harmful to the health of the animal or toxic to the animal.

The foregoing has outlined rather broadly the features and technical advantages of the present application in order that the detailed description that follows may be better understood. Additional features and advantages of the application will be described hereinafter which form the subject of the claims of the application. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present application. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the application as set forth in the appended claims. The novel features which are believed to be characteristic of the application, both as to its organization and method of operation, together with further objects and advantages will be better understood from the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows canine bitter taste receptor (T2R) nucleotide sequences (SEQ ID NOs: 1-16) along with their corresponding amino acid sequences (SEQ ID NOs: 17-32). The sequences include the canine bitter taste receptors cT2R1, cT2R2, cT2R3, cT2R4, cT2R5, cT2R7, cT2R10, cT2R12, cT2R38, cT2R39, cT2R40, cT2R41, cT2R42, cT3R43, cT2R62, and cT2R67.

FIG. 2 shows canine T2R sequence alignments. The dashed grey arrows indicate active site positions occupied by mostly asparagine or serine residues. The solid black arrows indicate structural tryptophan residues that are present in all human and cat bitter receptors as well as all canine bitter receptors except T2R12. The dashed black arrows indicate the conserved asparagine which is present in most of the bitter receptors. The conjoined solid arrows indicate the conserved LxxxR motif (IxxxR for some instances in T2R2), wherein x can be any amino acid. The conjoined dashed arrows indicate the conserved LxxSL motif.

FIG. 3A-E shows (A) the chemical structure of Menthol, (B) in silico modeling of Menthol docked within the active site of the canine T2R1, (C) a close-up view of selected residues lining the active site pocket interacting with, or close to, Menthol, (D) a ligand interaction map demonstrating potential interaction sites between Menthol and T2R1 and (E) a dose-response curve for Menthol when tested against canine T2R1 in vitro. Asn89 can potentially make a hydrogen bond interaction with the ligand. Other residues that can potentially make hydrogen bonding interactions, pi interactions, or charged interactions with the ligand include Tyr239. Residues that can potentially make van der Waals interactions with the ligand include Ile167, Gln174, Glu169, Phe257, Ala242, Phe177, His238, Cys260, Phe264, Leu234, Cys235, Phe85, Leu261, Leu178, Leu181, Va186, and Phe82.

-   -   The backbone of the protein is represented as a ribbon to depict         the helical nature of the seven transmembrane-helix structure of         the receptor. The ligand is shown in space-filling CPK format         (Corey et al., Rev Sci Instrum, 24(8): 621-627 (1953)). In this         and later FIGS. 3-9) hydrogen bond interactions with the ligand         are shown in dotted lines, while salt-bridge and other         interactions are shown as solid lines. For the interaction maps         hydrogen bonding and other specific interactions are shown as         arrows, while residues forming a contact with the ligand are         represented as circles. Darker circles represent residues with         van der Waals interactions with the ligand, while lighter         circles represent residues with polar, hydrogen bonding, Pi         interactions, or charged interactions with the ligand. A lighter         outer circle around a residue, if present, signals a large         change in its solvent accessible surface when the ligand binds.         More residues are shown in the schematic interaction maps in (D)         than in the 3D model views in (C), since including all of the         residues in (C) would obscure the view of the ligand.     -   During ligand binding and receptor activation, active site         rearrangements occur. As such, modeled interactions are dynamic,         and may be formed or break dynamically, and may be replaced with         other interactions in the vicinity of the ligand during these         processes.

FIG. 4A-E shows (A) the chemical structure of Ofloxacin, (B) in silico modeling of Ofloxacin docked within the active site of the canine T2R2, (C) a close-up view of selected residues lining the active site pocket interacting with, or close to, Ofloxacin, (D) a ligand interaction map demonstrating potential interaction sites between Ofloxacin and T2R2 and (E) a dose-response curve for Ofloxacin when tested against canine T2R2 in vitro. Residues that can potentially make hydrogen bond or salt bridge interactions with the ligand include Ser94, Trp90, Lys268, Tyr245, and Glu180. Additional residues that can potentially make polar, hydrogen bonding, pi interactions, or charged interactions with the ligand include Arg176 and Met91. Additional residues that can potentially make van der Waals interactions with the ligand include Asn185, Val184, Met181, Phe249, Pro155, Gln177, Lys174, Phe264, Phe93, Leu59, Met271, Phe246, and Leu188.

FIG. 5A-E shows (A) the chemical structure of Chloroquine, (B) in silico modeling of Chloroquine docked within the active site of the canine T2R3, (C) a close-up view of selected residues lining the active site pocket interacting with, or close to, Chloroquine, (D) a ligand interaction map demonstrating potential interaction sites between Chloroquine and T2R3 and (E) a dose-response curve for Chloroquine when tested against canine T2R3 in vitro. Residues that can make hydrogen bonding or charged interactions with the ligand include Asn93 and Asp86. Additional residues that can make polar, hydrogen bonding, pi interactions, or charged interactions with the ligand include Tyr246, Phe247, Thr186, Asn189, Trp89, and Arg175. Additional residues making primarily van der Waals interactions with the ligand include Phe250, Gly185, Phe243, Thr90, Asn176, Val149, Ile154, Lys174, Met82, Ile85, Lys173, and Met69.

FIG. 6A-E shows (A) the chemical structure of Colchicine, (B) in silico modeling of Colchicine docked within the active site of the canine T2R4, (C) a close-up view of selected residues lining the active site pocket interacting with, or close to, Colchicine, (D) a ligand interaction map demonstrating potential interaction sites between Colchicine and T2R4 and (E) a dose-response curve for Colchicine when tested against canine T2R4 in vitro. Ser186, Asp93, and Tyr240 can potentially make a hydrogen bond with the ligand. Additional residues that can potentially make polar, hydrogen bonding, pi interactions, or charged interactions with the ligand include Ser94, Leu97, Asn95, Leu92, Ser96, Trp98, Val187, and Thr247. Residues that can potentially make van der Waals interactions with the ligand include Tyr243, Trp89, Met58, Ser269, Pro273, Ser270, Gln189, Thr144, Leu188, Val183, Leu182, Ser244, and Met90.

FIG. 7A-E shows (A) the chemical structure of 1, 10 Phenanthroline, (B) in silico modeling of 1,10 Phenanthroline docked within the active site of the canine T2R5, (C) a close-up view of selected residues lining the active site pocket interacting with, or close to, 1, 10 Phenanthroline, (D) a ligand interaction map demonstrating potential interaction sites between 1,10 Phenanthroline and T2R5 and (E) a dose-response curve for 1, 10 Phenanthroline when tested against canine T2R5 in vitro. There is a potential hydrogen bond between Ser89 and each nitrogen of 1, 10 Phenanthroline. Additional residues that can potentially make van der Waals or Pi interactions with the ligand include Pro264, Leu58, Va188, Gln90, Ile86, Leu173, Trp165, Thr258, Ala261, Tyr234, Glu257, Met260, and Trp85.

FIG. 8A-E shows (A) the chemical structure of Cucurbitacin B, (B) in silico modeling of Cucurbitacin B docked within the active site of the canine T2R10, (C) a close-up view of selected residues lining the active site pocket interacting with, or close to, Cucurbitacin B, (D) a ligand interaction map demonstrating potential interaction sites between Cucurbitacin B and T2R10 and (E) a dose-response curve for Cucurbitacin B when tested against canine T2R10 in vitro. Lys258 and Leu180 (backbone) can potentially make hydrogen bonds with the ligand. Additional residues that can potentially make polar, hydrogen bonding, pi interactions, or charged interactions with the ligand include Lys170, Glu172, and Asn181. Residues that can potentially make van der Waals interactions with the ligand include Phe261, Met265, Ile262, Gln169, Lys69, Met168, Ile245, Va190, Phe242, Gln94, Val184, Asn93, Trp89, and Tyr241.

FIG. 9A-E shows (A) the chemical structure of Propylthiouracil, (B) in silico modeling of Propylthiouracil docked within the active site of the canine T2R43, (C) a close-up view of selected residues lining the active site pocket interacting with, or close to, Propylthiouracil, (D) a ligand interaction map demonstrating potential interaction sites between Propylthiouracil and T2R43 and (E) a dose-response curve for Propylthiouracil when tested against canine T2R43 in vitro. Residues that can potentially make hydrogen bond or charged interactions with the ligand include Tyr241, Trp88, and Thr181. Additional residues that can potentially make polar, hydrogen bonding, pi interactions, or charged interactions with the ligand include Met177, Asn92, Asn184, and Phe185. Additional residues that can potentially make van der Waals interactions with the ligand include Gln152, His143, Phe261, Ala172, His85, Asp170, Lys265, Phe242, Leu245, Thr89, and Phe180.

FIG. 10 shows a summary table of receptor-ligand interactions detailed in FIGS. 3-9. (+) indicates that the ligand elicited a clear dose dependent response from the receptor in vitro; (−) indicates that the ligand did not elicit a response specific, dose dependent response from the receptor in vitro; and shaded cells indicate the interactions detailed in FIGS. 3-9.

DETAILED DESCRIPTION

The presently disclosed subject matter relates to methods for screening and identifying compounds that modulate the activity and/or expression of bitter taste receptors. The presently disclosed subject matter further relates to making palatable, nutritionally-complete pet food products and medicines, wherein the raw materials of the pet food and/or finalized pet food product or medicine is screened to determine if it contains compounds that modulate the bitter taste receptors. Furthermore, such screening methods can be used to select raw materials and/or finalized pet food products that do not comprise bitter receptor activating compounds. Compounds identified through said methods can be used to modify the palatability of pet food products and medicines by increasing or decreasing a bitter taste. Said compounds can also be used to increase a bitter taste of an object, and thereby reduce palatability and ingestion by a dog.

1. Definitions

The terms used in this specification generally have their ordinary meanings in the art, within the context of this invention and in the specific context where each term is used. Certain terms are discussed below, or elsewhere in the specification, to provide additional guidance to the practitioner in describing the methods and compositions of the invention and how to make and use them.

As used herein, the use of the word “a” or “an” when used in conjunction with the term “comprising” in the claims and/or the specification may mean “one,” but it is also consistent with the meaning of “one or more,” “at least one,” and “one or more than one.” Still further, the terms “having,” “including,” “containing” and “comprising” are interchangeable and one of skill in the art is cognizant that these terms are open ended terms.

The term “about” or “approximately” means within an acceptable error range for the particular value as determined by one of ordinary skill in the art, which will depend in part on how the value is measured or determined, i.e., the limitations of the measurement system. For example, “about” can mean within 3 or more than 3 standard deviations, per the practice in the art. Alternatively, “about” can mean a range of up to 20%, preferably up to 10%, more preferably up to 5%, and more preferably still up to 1% of a given value. Alternatively, particularly with respect to biological systems or processes, the term can mean within an order of magnitude, preferably within 5-fold, and more preferably within 2-fold, of a value.

As used herein, “taste” refers to a sensation caused by activation of receptor cells in a subject's taste buds. In certain embodiments, taste can be selected from the group consisting of sweet, sour, salt, bitter, kokumi and umami. In certain embodiments, “taste” can include free fatty acid taste. See, e.g., Cartoni et al., J. of Neuroscience, 30(25): 8376-8382 (2010), the contents of which are incorporated herein by reference. In certain embodiments, a taste is elicited in a subject by a “tastant.” In certain embodiments, a tastant can be a synthetic tastant. In certain embodiments, the tastant is obtained or prepared from a natural source.

As used herein, “taste profile” refers to a combination of tastes, such as, for example, one or more of a sweet, sour, salt, bitter, umami, kokumi and free fatty acid taste. In certain embodiments, a taste profile is produced by one or more tastant that is present in a composition at the same or different concentrations. In certain embodiments, a taste profile refers to the intensity of a taste or combination of tastes, for example, a sweet, sour, salt, bitter, umami, kokumi and free fatty acid taste, as detected by a subject or any assay known in the art. In certain embodiments, modifying, changing or varying the combination of tastants in a taste profile can change the sensory experience of a subject.

As used herein, “flavor” refers to one or more sensory stimuli, such as, for example, one or more of taste (gustatory), smell (olfactory), touch (tactile) and temperature (thermal) stimuli. In certain non-limiting embodiments, the sensory experience of a subject exposed to a flavor can be classified as a characteristic experience for the particular flavor. For example, a flavor can be identified by the subject as being, but not limited to, a floral, citrus, berry, nutty, caramel, chocolate, peppery, smoky, cheesy, meaty, etc., flavor. As used herein, a flavor composition can be selected from a liquid, solution, dry powder, spray, paste, suspension and any combination thereof. The flavor can be a natural composition, an artificial composition, a nature identical, or any combination thereof.

As used interchangeably herein, “aroma” and “smell” refer to an olfactory response to a stimulus. For example, and not by way of limitation, an aroma can be produced by aromatic substances that are perceived by the odor receptors of the olfactory system.

As used herein, “flavor profile” refers to a combination of sensory stimuli, for example, tastes, such as sweet, sour, bitter, salty, umami, kokumi and free fatty acid tastes, and/or olfactory, tactile and/or thermal stimuli. In certain embodiments, the flavor profile comprises one or more flavors which contribute to the sensory experience of a subject. In certain embodiments, modifying, changing or varying the combination of stimuli in a flavor profile can change the sensory experience of a subject.

As used herein “admixing,” for example, “admixing the flavor composition or combinations thereof of the present application with a food product,” refers to the process where the flavor composition, or individual components of the flavor composition, is mixed with or added to the completed product or mixed with some or all of the components of the product during product formation or some combination of these steps. When used in the context of admixing, the term “product” refers to the product or any of its components. This admixing step can include a process selected from the step of adding the flavor composition to the product, spraying the flavor composition on the product, coating the flavor composition on the product, suspending the product in the flavor composition, painting the flavor composition on the product, pasting the flavor composition on the product, encapsulating the product with the flavor composition, mixing the flavor composition with the product and any combination thereof. The flavor composition can be a solution, liquid, dry powder, spray, paste, suspension and any combination thereof.

As used herein, “palatability” can refer to the overall willingness of a human or non-human animal, for example, a companion animal, to eat a certain food product. Increasing the “palatability” of a food product can lead to an increase in the enjoyment and acceptance of the food by the human or non-human animal to ensure the human or non-human animal eats a “healthy amount” of the food. Decreasing the “palatability” of a food product can lead to a decrease in the enjoyment and acceptance of the food by the human or non-human animal. The term “healthy amount” of a food as used herein refers to an amount that enables the human or non-human animal to maintain or achieve an intake contributing to its overall general health in terms of micronutrients, macronutrients and calories, for example, such as set out in the “Mars Petcare Essential Nutrient Standards.” In certain embodiments, “palatability” can mean a relative preference of a human or non-human animal for one food product over another. For example, when a human or non-human animal shows a preference for one of two or more food products, the preferred food product is more “palatable,” and has “enhanced palatability.” In certain embodiments, the relative palatability of one food product compared to one or more other food products can be determined, for example, in side-by-side, free-choice comparisons, e.g., by relative consumption of the food products, or other appropriate measures of preference indicative of palatability. Palatability can be determined by a standard testing protocol in which the animal has equal access to both food products such as a test called “two-bowl test” or “versus test.” Such preference can arise from any of the animal's senses, but can be related to, inter alia, taste, aftertaste, smell, mouth feel and/or texture.

The term “pet food” or “pet food product” or “final pet food product” means a product or composition that is intended for consumption by a companion animal, such as cats, dogs, guinea pigs, rabbits, birds and horses. For example, but not by way of limitation, the companion animal can be a “domestic” dog, e.g., Canis lupus familiaris. In certain embodiments, the companion animal can be a “domestic” cat such as Felis domesticus. A “pet food” or “pet food product” includes any food, feed, snack, food supplement, liquid, beverage, treat, toy (chewable and/or consumable toys), meal substitute or meal replacement.

The term “human food” or “human food product” or “final human food product” means a product or composition that is intended for consumption by a human. A “human food” or “human food product” includes any food, feed, snack, food supplement, liquid, beverage, treat, meal substitute or meal replacement.

In certain embodiments, a “food product” includes human and/or pet food products.

As used herein “nutritionally-complete” refers to pet food product that contains all known required nutrients for the intended recipient of the pet food product, in appropriate amounts and proportions based, for example, on recommendations of recognized or competent authorities in the field of companion animal nutrition. Such foods are therefore capable of serving as a sole source of dietary intake to maintain life, without the addition of supplemental nutritional sources.

The term “raw material” means a plant and/or animal material before being processed or manufactured into a final pet food product. In certain embodiments, a “raw material” is not significantly processed in order to separate it into individual elements prior to analysis (e.g., by extraction, purification, fractionation and/or concentration). A “raw material” includes a protein source for a pet food product. In certain embodiments, the raw material is a novel protein source that does not compete with the human food sources (i.e., a protein source that is not commonly eaten by humans). In certain embodiments, the raw material is a by-product of the human food chain. In certain non-limiting embodiments, the “raw material” is processed, for example, in order to separate it into individual elements prior to analysis (e.g., by extraction, purification, fractionation and/or concentration), prior to being analyzed according to the methods described herein.

As used herein “flavor composition” refers to at least one compound or biologically acceptable salt thereof that modulates, including enhancing, multiplying, potentiating, decreasing, suppressing, or inducing, the tastes, smells, flavors and/or textures of a natural or synthetic tastant, flavoring agent, taste profile, flavor profile and/or texture profile in an animal or a human. In certain embodiments, the flavor composition comprises a combination of compounds or biologically acceptable salts thereof. In certain embodiments, the flavor composition includes one or more excipients.

As used herein, “taste deterrent,” “taste deterrent product,” or “taste deterrent composition” refers to a product or composition containing at least one compound or biologically acceptable salt thereof that provides a bitter taste to an object. In certain embodiments, the taste deterrent discourages an animal from chewing, licking, or consuming an object, for example, a food or liquid product. In certain embodiments, the object is, for example but not limited to, clothing, shoes, carpet, furniture, household items, pesticides, herbicides, or poisonous compounds. In certain embodiments, the object is another animal or the animal itself. In other embodiment, the object is toxic to the animal, or would be detrimental to the animal's health upon ingestion.

As used herein, the terms “modulates” or “modifies” refers to an increase or decrease in the amount, quality or effect of a particular activity of a receptor and/or an increase or decrease in the expression, activity or function of a receptor. “Modulators,” as used herein, refer to any inhibitory or activating compounds identified using in silico, in vitro and/or in vivo assays for, e.g., agonists, antagonists, allosteric modulators and their homologs, including fragments, variants and mimetics.

“Inhibitors” or “antagonists,” as used herein, refer to modulating compounds that reduce, decrease, block, prevent, delay activation, inactivate, desensitize or down regulate the biological activity and/or expression of a receptor or pathway of interest. The term “antagonist” includes full, partial, and neutral antagonists as well as inverse agonists.

“Inducers,” “activators” or “agonists,” as used herein, refer to modulating compounds that increase, induce, stimulate, open, activate, facilitate, enhance activation, sensitize or upregulate a receptor or pathway of interest. The term “agonist” includes full and partial agonists.

“Allosteric modulators” as used herein, refer to “positive allosteric modulators” and “negative allosteric modulators.” “Positive allosteric modulators” refer to modulating compounds that increase, induce, stimulate, open, activate, facilitate, enhance activation, sensitize or up regulate a receptor or pathway of interest caused by the binding of a different compound to the receptor. “Negative allosteric modulators” refer to modulating compounds that reduce, decrease, block, prevent, delay activation, inactivate, desensitize or down regulate the biological activity and/or expression of a receptor or pathway of interest caused by the binding of a different compound to the receptor.

As used herein, the terms “vector” and “expression vector” refer to DNA molecules that are either linear or circular, into which another DNA sequence fragment of appropriate size can be integrated. Such DNA fragment(s) can include additional segments that provide for transcription of a gene encoded by the DNA sequence fragment. The additional segments can include and are not limited to: promoters, transcription terminators, enhancers, internal ribosome entry sites, untranslated regions, polyadenylation signals, selectable markers, origins of replication and such like. Expression vectors are often derived from plasmids, cosmids, viral vectors and yeast artificial chromosomes. Vectors are often recombinant molecules containing DNA sequences from several sources.

The term “operably linked,” when applied to DNA sequences, for example in an expression vector, indicates that the sequences are arranged so that they function cooperatively in order to achieve their intended purposes, i.e., a promoter sequence allows for initiation of transcription that proceeds through a linked coding sequence as far as the termination signal.

The term “nucleic acid molecule” and “nucleotide sequence,” as used herein, refers to a single or double stranded covalently-linked sequence of nucleotides in which the 3′ and 5′ ends on each nucleotide are joined by phosphodiester bonds. The nucleic acid molecule can include deoxyribonucleotide bases or ribonucleotide bases, and can be manufactured synthetically in vitro or isolated from natural sources.

The terms “polypeptide,” “peptide,” “amino acid sequence” and “protein,” used interchangeably herein, refer to a molecule formed from the linking of at least two amino acids. The link between one amino acid residue and the next is an amide bond and is sometimes referred to as a peptide bond. A polypeptide can be obtained by a suitable method known in the art, including isolation from natural sources, expression in a recombinant expression system, chemical synthesis or enzymatic synthesis. The terms can apply to amino acid polymers in which one or more amino acid residue is an artificial chemical mimetic of a corresponding naturally occurring amino acid, as well as to naturally occurring amino acid polymers and non-naturally occurring amino acid polymers.

The term “amino acid,” as used herein, refers to naturally occurring and synthetic amino acids, as well as amino acid analogs and amino acid mimetics that function in a manner similar to the naturally occurring amino acids. Naturally occurring amino acids are those encoded by the genetic code, as well as those amino acids that are later modified, e.g., hydroxyproline, gamma-carboxyglutamate and 0-phosphoserine. Amino acid analogs and derivatives can refer to compounds that have the same basic chemical structure as a naturally occurring amino acid, i.e., a carbon that is bound to a hydrogen, a carboxyl group, an amino group and an R group, e.g., homoserine, norleucine, methionine sulfoxide and methionine methyl sulfonium. Such analogs can have modified R groups (e.g., norleucine) or modified peptide backbones, but retain the same basic chemical structure as a naturally occurring amino acid. Amino acid mimetics means chemical compounds that have a structure that is different from the general chemical structure of an amino acid, but that function in a manner similar to a naturally occurring amino acid.

The terms “isolated” or “purified”, used interchangeably herein, refers to a nucleic acid, a polypeptide, or other biological moiety that is removed from components with which it is naturally associated. The term “isolated” can refer to a polypeptide that is separate and discrete from the whole organism with which the molecule is found in nature or is present in the substantial absence of other biological macromolecules of the same type. The term “isolated” with respect to a polynucleotide can refer to a nucleic acid molecule devoid, in whole or part, of sequences normally associated with it in nature; or a sequence, as it exists in nature, but having heterologous sequences in association therewith; or a molecule disassociated from the chromosome.

As used herein, the term “recombinant” can be used to describe a nucleic acid molecule and refers to a polynucleotide of genomic, RNA, DNA, cDNA, viral, semisynthetic or synthetic origin which, by virtue of its origin or manipulation is not associated with all or a portion of the polynucleotide with which it is associated in nature.

The term “fusion,” as used herein, refers to joining of different peptide or protein segments by genetic or chemical methods wherein the joined ends of the peptide or protein segments may be directly adjacent to each other or may be separated by linker or spacer moieties such as amino acid residues or other linking groups.

2. Bitter Taste Receptors

The presently disclosed subject matter provides bitter taste receptors for use in the disclosed methods. The bitter taste receptors of the present disclosure can include mammalian bitter taste receptors such as, but not limited to, canine bitter taste receptors.

In certain non-limiting embodiments, the bitter taste receptor is a canine bitter taste receptor, for example, canine bitter taste receptor T2R1, T2R2, T2R3, T2R4, T2R5, T2R7, T2R10, T2R12, T2R38, T2R39, T2R40, T2R41, T2R42, T2R43, T2R62, T2R67, or combinations thereof.

In certain embodiments, a bitter taste receptor for use in the presently disclosed methods encompasses a canine bitter taste receptor having the nucleotide sequence set forth in SEQ ID NO:1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, or 16 and/or the amino acid sequence set forth in SEQ ID NO:17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, or 32, including fragments thereof (e.g., functional fragments thereof) and variants thereof.

In certain non-limiting embodiments, a bitter taste receptor for use in the presently disclosed methods does not include a feline bitter taste receptor.

In certain embodiments, the bitter taste receptor for use in the presently disclosed subject matter can include a receptor encoded by a nucleotide sequence that is at least 85%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98% or at least 99% homologous to any one of SEQ ID NOs:1-16 (homology, as that term is used herein, may be measured using standard software such as BLAST or FASTA).

In certain embodiments, the bitter taste receptor for use in the presently disclosed methods can include a receptor comprising an amino acid sequence that is between about 33 and 99%, between about 34 and 99%, between about 35 and 99%, between about 40 and 99%, between about 45 and 99%, between about 50 and 99%, between about 55 and 99%, between about 60 and 99%, between about 61 and 99%, between about 65 and 99%, between about 70 and 99%, between about 72 and 99%, between about 75 and 99%, between about 79 and 99%, between about 80 and 99%, between about 84 and 99%, between about 85 and 99%, between about 87 and 99%, between about 89 and 99%, between about 90 and 99%, between about 95 and 99%, or between about 97 and 99% homologous to any one of SEQ ID NOs:17-32 (homology, as that term is used herein, may be measured using standard software such as BLAST or FASTA).

In certain embodiments, the bitter taste receptor for use in the presently disclosed methods can include a receptor comprising an amino acid sequence that is at least about 33%, 34%, 35%, 40%, 45%, 50%, 55%, 60%, 61%, 65%, 70%, 72%, 75%, 79%, 80%, 84%, 85%, 87%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% homologous to any one of SEQ ID NOs:17-32 (homology, as that term is used herein, may be measured using standard software such as BLAST or FASTA).

In certain embodiments, the bitter taste receptor is a canine T2R1 comprising an amino acid sequence as set forth in SEQ ID NO:17, or a sequence at least 99, 98, 97, 96, 95, 90, 85 or 80 percent homologous thereto (homology, as that term is used herein, may be measured using standard software such as BLAST or FASTA), and is encoded, for example, by a nucleic acid comprising a sequence as set forth in SEQ ID NO:1, or a sequence at least 99, 98, 97, 96, 95, 90, 85 or 80 percent homologous thereto (homology, as that term is used herein, may be measured using standard software such as BLAST or FASTA).

In certain embodiments, the bitter taste receptor is a canine T2R2 comprising an amino acid sequence as set forth in SEQ ID NO:18, or a sequence at least 99, 98, 97, 96, 95, 90, 85 or 80 percent homologous thereto (homology, as that term is used herein, may be measured using standard software such as BLAST or FASTA), and is encoded, for example, by a nucleic acid comprising a sequence as set forth in SEQ ID NO:2, or a sequence at least 99, 98, 97, 96, 95, 90, 85 or 80 percent homologous thereto (homology, as that term is used herein, may be measured using standard software such as BLAST or FASTA).

In certain embodiments, the bitter taste receptor is a canine T2R3 comprising an amino acid sequence as set forth in SEQ ID NO:19, or a sequence at least 99, 98, 97, 96, 95, 90, 85 or 80 percent homologous thereto (homology, as that term is used herein, may be measured using standard software such as BLAST or FASTA), and is encoded, for example, by a nucleic acid comprising a sequence as set forth in SEQ ID NO:3, or a sequence at least 99, 98, 97, 96, 95, 90, 85 or 80 percent homologous thereto (homology, as that term is used herein, may be measured using standard software such as BLAST or FASTA).

In certain embodiments, the bitter taste receptor is a canine T2R4 comprising an amino acid sequence as set forth in SEQ ID NOs:20, or a sequence at least 99, 98, 97, 96, 95, 90, 85 or 80 percent homologous thereto (homology, as that term is used herein, may be measured using standard software such as BLAST or FASTA), and is encoded, for example, by a nucleic acid comprising a sequence as set forth in SEQ ID NO:4, or a sequence at least 99, 98, 97, 96, 95, 90, 85 or 80 percent homologous thereto (homology, as that term is used herein, may be measured using standard software such as BLAST or FASTA).

In certain embodiments, the bitter taste receptor is a canine T2R5 comprising an amino acid sequence as set forth in SEQ ID NO:21, or a sequence at least 99, 98, 97, 96, 95, 90, 85 or 80 percent homologous thereto (homology, as that term is used herein, may be measured using standard software such as BLAST or FASTA), and is encoded, for example, by a nucleic acid comprising a sequence as set forth in SEQ ID NO:5, or a sequence at least 99, 98, 97, 96, 95, 90, 85 or 80 percent homologous thereto (homology, as that term is used herein, may be measured using standard software such as BLAST or FASTA).

In certain embodiments, the bitter taste receptor is a canine T2R7 comprising an amino acid sequence as set forth in SEQ ID NO:22, or a sequence at least 99, 98, 97, 96, 95, 90, 85 or 80 percent homologous thereto (homology, as that term is used herein, may be measured using standard software such as BLAST or FASTA), and is encoded, for example, by a nucleic acid comprising a sequence as set forth in SEQ ID NO:6, or a sequence at least 99, 98, 97, 96, 95, 90, 85 or 80 percent homologous thereto (homology, as that term is used herein, may be measured using standard software such as BLAST or FASTA).

In certain embodiments, the bitter taste receptor is a canine T2R10 comprising an amino acid sequence as set forth in SEQ ID NO:23, or a sequence at least 99, 98, 97, 96, 95, 90, 85 or 80 percent homologous thereto (homology, as that term is used herein, may be measured using standard software such as BLAST or FASTA), and is encoded, for example, by a nucleic acid comprising a sequence as set forth in SEQ ID NO:7, or a sequence at least 99, 98, 97, 96, 95, 90, 85 or 80 percent homologous thereto (homology, as that term is used herein, may be measured using standard software such as BLAST or FASTA).

In certain embodiments, the bitter taste receptor is a canine T2R12 comprising an amino acid sequence as set forth in SEQ ID NO:24, or a sequence at least 99, 98, 97, 96, 95, 90, 85 or 80 percent homologous thereto (homology, as that term is used herein, may be measured using standard software such as BLAST or FASTA), and is encoded, for example, by a nucleic acid comprising a sequence as set forth in SEQ ID NO:8, or a sequence at least 99, 98, 97, 96, 95, 90, 85 or 80 percent homologous thereto (homology, as that term is used herein, may be measured using standard software such as BLAST or FASTA).

In certain embodiments, the bitter taste receptor is a canine T2R38 comprising an amino acid sequence as set forth in SEQ ID NO:25, or a sequence at least 99, 98, 97, 96, 95, 90, 85 or 80 percent homologous thereto (homology, as that term is used herein, may be measured using standard software such as BLAST or FASTA), and is encoded, for example, by a nucleic acid comprising a sequence as set forth in SEQ ID NO:9, or a sequence at least 99, 98, 97, 96, 95, 90, 85 or 80 percent homologous thereto (homology, as that term is used herein, may be measured using standard software such as BLAST or FASTA).

In certain embodiments, the bitter taste receptor is a canine T2R39 comprising an amino acid sequence as set forth in SEQ ID NO:26, or a sequence at least 99, 98, 97, 96, 95, 90, 85 or 80 percent homologous thereto (homology, as that term is used herein, may be measured using standard software such as BLAST or FASTA), and is encoded, for example, by a nucleic acid comprising a sequence as set forth in SEQ ID NO:10, or a sequence at least 99, 98, 97, 96, 95, 90, 85 or 80 percent homologous thereto (homology, as that term is used herein, may be measured using standard software such as BLAST or FASTA).

In certain embodiments, the bitter taste receptor is a canine T2R40 comprising an amino acid sequence as set forth in SEQ ID NO:27, or a sequence at least 99, 98, 97, 96, 95, 90, 85 or 80 percent homologous thereto (homology, as that term is used herein, may be measured using standard software such as BLAST or FASTA), and is encoded, for example, by a nucleic acid comprising a sequence as set forth in SEQ ID NO:11, or a sequence at least 99, 98, 97, 96, 95, 90, 85 or 80 percent homologous thereto (homology, as that term is used herein, may be measured using standard software such as BLAST or FASTA).

In certain embodiments, the bitter taste receptor is a canine T2R41 comprising an amino acid sequence as set forth in SEQ ID NO:28, or a sequence at least 99, 98, 97, 96, 95, 90, 85 or 80 percent homologous thereto (homology, as that term is used herein, may be measured using standard software such as BLAST or FASTA), and is encoded, for example, by a nucleic acid comprising a sequence as set forth in SEQ ID NO:12, or a sequence at least 99, 98, 97, 96, 95, 90, 85 or 80 percent homologous thereto (homology, as that term is used herein, may be measured using standard software such as BLAST or FASTA).

In certain embodiments, the bitter taste receptor is a canine T2R42 comprising an amino acid sequence as set forth in SEQ ID NO:29, or a sequence at least 99, 98, 97, 96, 95, 90, 85 or 80 percent homologous thereto (homology, as that term is used herein, may be measured using standard software such as BLAST or FASTA), and is encoded, for example, by a nucleic acid comprising a sequence as set forth in SEQ ID NO:13, or a sequence at least 99, 98, 97, 96, 95, 90, 85 or 80 percent homologous thereto (homology, as that term is used herein, may be measured using standard software such as BLAST or FASTA).

In certain embodiments, the bitter taste receptor is a canine T2R43 comprising an amino acid sequence as set forth in SEQ ID NO:30, or a sequence at least 99, 98, 97, 96, 95, 90, 85 or 80 percent homologous thereto (homology, as that term is used herein, may be measured using standard software such as BLAST or FASTA), and is encoded, for example, by a nucleic acid comprising a sequence as set forth in SEQ ID NO:14, or a sequence at least 99, 98, 97, 96, 95, 90, 85 or 80 percent homologous thereto (homology, as that term is used herein, may be measured using standard software such as BLAST or FASTA).

In certain embodiments, the bitter taste receptor is a canine T2R62 comprising an amino acid sequence as set forth in SEQ ID NO:31, or a sequence at least 99, 98, 97, 96, 95, 90, 85 or 80 percent homologous thereto (homology, as that term is used herein, may be measured using standard software such as BLAST or FASTA), and is encoded, for example, by a nucleic acid comprising a sequence as set forth in SEQ ID NO:15, or a sequence at least 99, 98, 97, 96, 95, 90, 85 or 80 percent homologous thereto (homology, as that term is used herein, may be measured using standard software such as BLAST or FASTA).

In certain embodiments, the bitter taste receptor is a canine T2R67 comprising an amino acid sequence as set forth in SEQ ID NO:32, or a sequence at least 99, 98, 97, 96, 95, 90, 85 or 80 percent homologous thereto (homology, as that term is used herein, may be measured using standard software such as BLAST or FASTA), and is encoded, for example, by a nucleic acid comprising a sequence as set forth in SEQ ID NO:16, or a sequence at least 99, 98, 97, 96, 95, 90, 85 or 80 percent homologous thereto (homology, as that term is used herein, may be measured using standard software such as BLAST or FASTA).

In certain embodiments, homology is described as a percent identity between two sequences. The percent identity of two amino acid sequences or of two nucleotide sequences can be determined by aligning the sequences for optimal comparison purposes (e.g., gaps can be introduced in the first sequence for best alignment with the sequence) and comparing the amino acid residues or nucleotides at corresponding positions. The percent identity can be determined by the number of identical amino acid residues or nucleotides in the sequences being compared (e.g., % identity=number of identical positions/total number of positions×100).

The determination of percent identity between two sequences can be determined using a mathematical algorithm known to those of skill in the art. A non-limiting example of a mathematical algorithm for comparing two sequences is the algorithm of Karlin and Altschul (1990) Proc. Natl. Acad. Sci. USA 87:2264-2268, modified as in Karlin and Altschul (1993) Proc. Natl. Acad. Sci. USA 90:5873-5877, the disclosures of which are incorporated herein by reference in their entireties. The NBLAST and XBLAST programs of Altschul, et al. (1990) J. Mol. Biol. 215:403-410 have incorporated such an algorithm. BLAST nucleotide searches can be performed with the NBLAST program, for example, score=100, wordlength=12, to obtain nucleotide sequences homologous to nucleotide sequences of the invention. BLAST protein searches can be performed with the XBLAST program, for example, score=50, wordlength=3, to obtain amino acid sequences homologous to amino acid sequence of the invention. To obtain gapped alignments for comparison purposes, Gapped BLAST can be utilized as described in Altschul et al. (1997) Nucleic Acids Res. 25:3389-3402, the disclosure of which is incorporated herein by reference in its entirety. Alternatively, PSI-Blast can be used to perform an iterated search, which detects distant relationships between molecules. When utilizing BLAST, Gapped BLAST, and PSI-Blast programs, the default parameters of the respective programs (e.g., XBLAST and NBLAST) can be used. See http://www.ncbi.nlm.nih.gov. An additional non-limiting example of a mathematical algorithm utilized for the comparison of sequences is the algorithm of Myers and Miller, CABIOS (1989), the disclosure of which is incorporated herein by reference in its entirety. The ALIGN program (version 2.0), which is part of the CGC sequence alignment software package, has incorporated such an algorithm. Other non-limiting examples of algorithms for sequence analysis known in the art include ADVANCE and ADAM as described in Torellis and Robotti (1994) Comput. Appl. Biosci., 10:3-5; and FASTA described in Pearson and Lipman (1988) Proc. Natl. Acad. Sci. 85:2444-8, the disclosures of which are incorporated herein by reference in their entireties. Within FASTA, ktup is a control option that sets the sensitivity and speed of the search.

In certain embodiments, the disclosed subject matter provides for the use of an isolated or purified bitter taste receptor and/or variants and fragments thereof. The disclosed subject matter also encompasses the use of sequence variants. In certain embodiments, variation can occur in either or both the coding and non-coding regions of a nucleotide sequence of a bitter taste receptor. Variants can include a substantially homologous protein encoded by the same genetic locus in an organism, i.e., an allelic variant. Variants also encompass proteins derived from other genetic loci in an organism, e.g., canine, but having substantial homology to the bitter taste receptor, i.e., a homolog. Variants can also include proteins substantially homologous to the bitter taste receptor but derived from another organism, i.e., an ortholog. Variants also include proteins that are substantially homologous to the bitter taste receptor that are produced by chemical synthesis. Variants also include proteins that are substantially homologous to the bitter taste receptor that are produced by recombinant methods.

Orthologs, homologs and allelic variants can be identified using methods well known in the art. These variants can include a nucleotide sequence encoding a receptor that is at least about 60-65%, about 65-70%, about 70-75, about 80-85%, about 90-95%, about 95-99% or more homologous to the nucleotide sequence shown in any one of SEQ ID NOs:1-16, or fragments thereof. Such nucleic acid molecules can readily be identified as being able to hybridize under stringent conditions, to the nucleotide sequence shown in any one of SEQ ID NOs:1-16, or a fragment thereof. In certain embodiments, two polypeptides (or regions thereof) are substantially homologous when the amino acid sequences are at least about 60-65%, about 65-70%, about 70-75, about 80-85%, about 90-95%, about 95-99% or more homologous to the amino acid sequences shown in any one of SEQ ID NOs:17-32, or a fragment thereof. A substantially homologous amino acid sequence, according to the disclosed subject matter, will be encoded by a nucleic acid sequence hybridizing to the nucleic acid sequence, or portion thereof, of the nucleotide sequence shown in any one of SEQ ID NOs:1-16 under stringent conditions.

The bitter taste receptors for use in the methods of the disclosed subject matter include bitter taste receptors having additions, deletions or substitutions of amino acid residues (variants) which do not substantially alter the biological activity of the receptor. Those individual sites or regions of the bitter taste receptors which may be altered without affecting biological activity can be determined by examination of the structure of the bitter taste receptor extracellular domain, for example. Alternatively and/or additionally, one can empirically determine those regions of the receptor which would tolerate amino acid substitutions by alanine scanning mutagenesis (Cunningham et al., Science 244, 1081-1085 (1989), the disclosure of which is hereby incorporated by reference in its entirety). In the alanine scanning mutagenesis method, selected amino acid residues are individually substituted with a neutral amino acid (e.g., alanine) in order to determine the effects on biological activity.

It is generally recognized that conservative amino acid changes are least likely to perturb the structure and/or function of a polypeptide. Accordingly, the disclosed subject matter encompasses one or more conservative amino acid changes within a bitter taste receptor. Conservative amino acid changes generally involve substitution of one amino acid with another that is similar in structure and/or function (e.g., amino acids with side chains similar in size, charge and shape). Families of amino acid residues having similar side chains have been defined in the art. These families include amino acids with basic side chains (e.g., lysine, arginine, histidine), acidic side chains (e.g., aspartic acid, glutamic acid), uncharged polar side chains (e.g., glycine, asparagine, glutamine, serine, threonine, tyrosine, cysteine, tryptophan), nonpolar side chains (e.g., alanine, valine, leucine, isoleucine, proline, phenylalanine, methionine), beta-branched side chains (e.g., threonine, valine, isoleucine) and aromatic side chains (e.g., tyrosine, phenylalanine, tryptophan, histidine). In certain embodiments, one or more amino acid residues within a bitter taste receptor can be replaced with other amino acid residues from the same side chain family and the altered protein can be tested for retained function using the functional assays described herein. Modifications can be introduced into a bitter taste receptor of the present disclosure by standard techniques known in the art, such as site-directed mutagenesis and PCR-mediated mutagenesis. If such substitutions result in a retention in biological activity, then more substantial changes can be introduced and/or other additions/deletions may be made and the resulting products screened. In certain embodiments, deletions or additions can be from 5-10 residues, alternatively from 2-5 amino acid residues or from 1-2 residues, and values in between.

The disclosed subject matter also provides for fusion proteins that comprise a bitter taste receptor, or fragment thereof. In certain embodiments, the disclosed subject matter provides for fusion proteins of a bitter taste receptor, or functional fragments thereof, and an immunoglobulin heavy chain constant region. In certain embodiments, a fusion protein of the present disclosure can include a detectable marker, a functional group such as a carrier, a label, a stabilizing sequence or a mechanism by which bitter taste receptor agonist binding can be detected. Non-limiting embodiments of a label include a FLAG tag, a His tag, a MYC tag, a maltose binding protein and others known in the art. The presently disclosed subject matter also provides nucleic acids encoding such fusion proteins, vectors containing fusion protein-encoding nucleic acids and host cells comprising such nucleic acids or vectors. In certain embodiments, fusions can be made at the amino terminus (N-terminus) of a bitter taste receptor or at the carboxy terminus (C-terminus) of a bitter taste receptor.

In certain embodiments, the bitter taste receptors disclosed herein can contain additional amino acids at the N-terminus and/or at the C-terminus end of the sequences, e.g., when used in the methods of the disclosed subject matter. In certain embodiments, the additional amino acids can assist with immobilizing the polypeptide for screening purposes, or allow the polypeptide to be part of a fusion protein, as disclosed above, for ease of detection of biological activity.

3. Methods for Identifying Bitter Taste Receptor Modulating Compounds

The present disclosure further provides methods for identifying compounds that modulate the activity and/or expression of a bitter taste receptor. For example, and not by way of limitation, the modulator can be an agonist (for example, a full or partial agonist), or an antagonist, or an inverse agonist, or an allosteric modulator. The presently disclosed subject matter provides in silico and in vitro methods for identifying compounds that modulate the activity and/or expression of a bitter taste receptor, disclosed above.

3.1 In Silico Methods

The presently disclosed subject matter further provides in silico methods for identifying compounds that can potentially interact with a bitter taste receptor and/or modulate the activity and/or expression of a bitter taste receptor.

In certain embodiments, the method can include predicting the three-dimensional structure (3D) of a bitter taste receptor and screening the predicted 3D structure with putative bitter taste receptor modulating compounds (i.e., test compounds). The method can further include predicting whether the putative compound would interact with the binding site of the receptor by analyzing the potential interactions with the putative compound and the amino acids of the receptor. The method can further include identifying a test compound that can bind to and/or modulate the biological activity of the bitter taste receptor by determining whether the 3D structure of the compound fits within the binding site of the 3D structure of the receptor.

In certain embodiments, the bitter taste receptor for use in the disclosed method can be a canine T2R1, T2R2, T2R3, T2R4, T2R5, T2R7, T2R10, T2R12, T2R38, T2R39, T2R40, T2R41, T2R42, T2R43, T2R62, T2R67, or combinations thereof.

In other embodiments, the bitter taste receptor for use in the disclosed method can have the amino acid sequence of any one of SEQ ID NO:17-32, or a fragment or variant thereof. In certain embodiments, the bitter taste receptor for use in the presently disclosed subject matter can include a receptor comprising an amino acid sequence having at least about 33%, 34%, 35%, 40%, 45%, 50%, 55%, 60%, 61%, 65%, 70%, 72%, 75%, 79%, 80%, 84%, 85%, 87%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% identity to any one of SEQ ID NO:17-32, or a fragment or variant thereof. In certain embodiments, the bitter taste receptor for use in the disclosed method can be encoded by a nucleotide sequence of any one of SEQ ID NO:1-16, or a fragment or variant thereof. In certain embodiments, the bitter taste receptor for use in the presently disclosed subject matter can include a receptor encoded by a nucleotide sequence having at least 85%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98% or at least 99% identity to any one of SEQ ID NO:1-16, or a fragment or variant thereof.

Non-limiting examples of compounds (e.g., potential bitter taste receptor modulators) that can be tested using the disclosed methods include any small chemical compound, or any biological entity, such as peptides, salts, amino acids and bitter compound known in the art, e.g. denatonium benzoate. In certain embodiments, the test compound can be a small chemical molecule.

In certain embodiments, structural models of a bitter taste receptor can be built using crystal structures of other GPCRs as templates for homology modeling. For example, and not by way of limitation, structural models can be generated using the crystal structures of Group 1 GPCRs. Bitter receptors belong to a separate subclass of GPCR's for which crystal structures have not been solved yet. In certain embodiments, a structural model of a bitter taste receptor can be based on a known or a combination of known crystal structures of GPCRs. (See, e.g., Lee et al., Eur J Pharmacol. 2015 May 14. pii: S0014-2999(15)30012-1, which is incorporated by reference in its entirety herein). In certain embodiments, a structural model of a bitter taste receptor can be generated based on the crystal structure of a β2 adrenergic receptor, 3SN6 from Protein Data Bank (PDB). (See, e.g., Rasmussen et al., Nature. 2011 Jul. 19; 477(7366):549-55, which is incorporated by reference in its entirety herein). In certain embodiments, a structural model of the 7 transmembrane domain (7TM) of a bitter taste receptor can be generated based on the crystal structures of existing GPCR crystal structure 3SN6 from PDB.

Any suitable modeling software known in the art can be used. In certain embodiments, the Modeller software package can be used to generate the three-dimensional protein structure.

In certain embodiments, the in silico methods of identifying a compound that binds to a T2R comprises determining whether a test compound interacts with one or more amino acids of a T2R binding pocket, as described herein.

Compounds that are identified by the disclosed in silico methods can be further tested using the in vitro and in vivo methods disclosed herein.

3.2 T2R Transmembrane Compound Binding Site

The present application provides for methods of screening for compounds that modulate the activity of a bitter taste receptor, for example, a canine T2R receptor, wherein the compounds interact with one or more amino acids of the bitter taste receptor. In certain embodiments, the binding site of a bitter taste receptor comprises amino acids within the 7TM domain of the receptor, and can be identified by generating an interaction map of the receptor using in silico modeling, as described herein. In one non-limiting example, the presence of an amino acid in the 7TM interaction map means that the residue is in the vicinity of the ligand binding environment, an interacts with the ligand.

In certain embodiments, the interaction between an amino acid in the 7TM interaction map and the ligand is a pi-pi interaction.

In certain embodiments, the interaction between an amino acid in the 7TM interaction map and the ligand is a hydrogen bond interaction.

In certain embodiments, the interaction between an amino acid in the 7TM interaction map and the ligand is a hydrophobic interaction.

In certain embodiments, the interaction between an amino acid in the 7TM interaction map and the ligand is a van de Waals interaction.

In certain embodiments, the amino acid in the 7TM interaction map is a polar amino acid, wherein the amino acid interacts with the ligand as a hydrogen bond donor and/or acceptor.

In certain embodiments, the interaction between a compound and one or more amino acids of the T2R receptors described herein can comprises one or more hydrogen bond, covalent bond, non-covalent bond, salt bridge, physical interaction, and combinations thereof. The interactions can also be any interaction characteristic of a ligand receptor interaction known in the art. Such interactions can be determined by, for example, site directed mutagenesis, x-ray crystallography, x-ray or other spectroscopic methods, Nuclear Magnetic Resonance (NMR), cross-linking assessment, mass spectroscopy or electrophoresis, cryo-microscopy, displacement assays based on known agonists, structural determination and combinations thereof. In certain embodiments, the interactions are determined in silico, for example, by theoretical means such as docking a compound into a canine T2R binding pocket using molecular docking, molecular modeling, molecular simulation, or other means known to persons of ordinary skill in the art. In certain embodiments, the T2R receptor is a canine T2R, for example, but not limited to, T2R1, T2R2, T2R3, T2R4, T2R5, T2R7, T2R10, T2R12, T2R38, T2R39, T2R40, T2R41, T2R42, T2R43, T2R62, and T2R67.

In certain embodiments, the T2R is a T2R present in canine but not present in feline animals, for example, T2R5, T2R39, T2R40, T2R41, and/or T2R62.

In certain embodiments, the compounds interact with one or more T2R receptors described herein according to any combination of interactions described herein, for example, one, two, three or more of the interactions.

In certain embodiments, the compounds bind to at least one of the receptors described herein. In certain embodiment, the compounds bind selectively to only one of the receptors described herein.

In one embodiment, the bitter taste receptor is a canine T2R1. In certain embodiments, the amino acids that the compounds interact with comprise Asn89 and/or Tyr239, for example, by polar or hydrogen bonding, as exemplified by in silico modeling of Menthol in T2R1 (FIG. 3). Alternatively, or in addition, in certain embodiments, the amino acids that the compounds interact with comprise any one, two, three or more of the T2R1 residues Asn89, Tyr239, Ile167, Gln174, Glu169, Phe257, Ala242, Phe177, His238, Cys260, Phe264, Leu234, Cys235, Phe85, Leu261, Leu178, Leu181, Va186, and Phe82, for example, by polar, hydrogen bond, salt bridge, van der Waals, pi, or other interactions, as exemplified by in silico modeling of Menthol in T2R1 (FIG. 3).

In one embodiment, the bitter taste receptor is a canine T2R2, which is shared by dogs and cats, but not humans, where it is a pseudogene. In certain embodiments, the amino acids that the compounds interact with comprise one or more of T2R2 residues Ser94, Trp90, Lys268, Tyr245, and/or Glu180, for example, by hydrogen bonding or salt bridge interactions, as exemplified by in silico modeling of Ofloxacin in T2R2 (FIG. 4). Alternatively, or in addition, in certain embodiments, the amino acids that the compounds interact with comprise T2R2 residues Arg176 and/or Met91, either alone or in conjunction with interactions listed above, for example, by polar, hydrogen bonding, or charged interactions, as exemplified by in silico modeling of Ofloxacin in T2R2 (FIG. 4). Alternatively, or in addition, in certain embodiments, the amino acids that the compounds interact with comprise any one, two, three or more of the T2R2 residues Ser94, Trp90, Lys268, Tyr245, Glu180, Arg176, Met91, Asn185, Val184, Met181, Phe249, Pro155, Gln177, Lys174, Phe264, Phe93, Leu59, Met271, Phe246, and Leu188, for example, by polar, hydrogen bond, salt bridge, van der Waals, pi, or other interactions, as exemplified by in silico modeling of Ofloxacin in T2R2 (FIG. 4).

In one embodiment, the bitter taste receptor is a canine T2R3. In certain embodiments, the amino acids that the compounds interact with comprise T2R3 residues Asn93 and/or Asp86, for example, by hydrogen bonding or salt bridge interactions, as exemplified by in silico modeling of Chloroquine in T2R3 (FIG. 5). Alternatively, or in addition, in certain embodiments, the amino acids that the compounds interact with comprise any one or more of the T2R3 residues Tyr246, Phe247, Thr186, Asn189, Trp89, Asp86, and Arg175, either alone or in conjunction with interactions listed above, for example, by polar, hydrogen bonding, or charged interactions, as exemplified by in silico modeling of Chloroquine in T2R3 (FIG. 5). Alternatively, or in addition, in certain embodiments, the amino acids that the compounds interact with comprise any one, two, three or more of the T2R3 residues Asn93, Asp86, Tyr246, Phe247, Thr186, Asn189, Trp89, Asp86, Arg175, Phe250, Gly185, Phe243, Thr90, Asn176, Val149, Ile154, Lys174, Met82, Ile85, Lys173, and Met69, for example, by polar, hydrogen bond, salt bridge, van der Waals, pi, or other interactions, as exemplified by in silico modeling of Chloroquine in T2R3 (FIG. 5).

In one embodiment, the bitter taste receptor is a canine T2R4. In certain embodiments, the amino acids that the compounds interact with comprise any one or more of T2R4 residues Ser186, Asp93, and Tyr240, for example, by hydrogen bonding or salt bridge interactions, as exemplified by in silico modeling of Colchicine in T2R4 (FIG. 6). Alternatively, or in addition, in certain embodiments, the amino acids that the compounds interact with comprise any one or more of T2R4 residues Ser94, Leu97, Asn95, Leu92, Ser96, Trp98, Val187, and Thr247, either alone or in conjunction with interactions listed above, for example, by polar, hydrogen bonding, or charged interactions, as exemplified by in silico modeling of Colchicine in T2R4 (FIG. 6). Alternatively, or in addition, in certain embodiments, the amino acids that the compounds interact with comprise any one, two, three or more of the T2R4 residues Ser186, Asp93, Tyr240, Ser94, Leu97, Asn95, Leu92, Ser96, Trp98, Val187, Thr247, Tyr243, Trp89, Met58, Ser269, Pro273, Ser270, Gln189, Thr144, Leu188, Val183, Leu182, Ser244, and Met90, for example, by polar, hydrogen bond, salt bridge, van der Waals, pi, or other interactions, as exemplified by in silico modeling of Colchicine in T2R4 (FIG. 6).

In one embodiment, the bitter taste receptor is a canine T2R5, which is present in dogs and humans, but not cats. In certain embodiments, the amino acids that the compounds interact with comprise T2R5 residue Ser89, for example, by hydrogen bonding or salt bridge interactions, as exemplified by in silico modeling of 1,10 Phenanthroline in T2R5 (FIG. 7). Alternatively, or in addition, in certain embodiments, the amino acids that the compounds interact with comprise any one, two, three or more of the T2R5 residues Ser89, Pro264, Leu58, Va188, Gln90, Ile86, Leu173, Trp165, Thr258, Ala261, Tyr234, Glu257, Met260, and Trp85, for example, by polar, hydrogen bond, salt bridge, van der Waals, pi, or other interactions, as exemplified by in silico modeling of 1,10 Phenanthroline in T2R5 (FIG. 7).

In one embodiment, the bitter taste receptor is a canine T2R10. In certain embodiments, the amino acids that the compounds interact with comprise T2R10 residues Lys258 and/or Leu180 (backbone), for example, by hydrogen bonding or salt bridge interactions, as exemplified by in silico modeling of Cucurbitacin B in T2R10 (FIG. 8). Alternatively, or in addition, in certain embodiments, the amino acids that the compounds interact with comprise one or more of T2R10 residues Lys170, Glu172, and Asn181, either alone or in conjunction with interactions listed above, for example, by polar, hydrogen bonding, or charged interactions, as exemplified by in silico modeling of Cucurbitacin B in T2R10 (FIG. 8). Alternatively, or in addition, in certain embodiments, the amino acids that the compounds interact with comprise any one, two, three or more of the T2R10 residues Lys258, Leu180, Lys170, Glu172, Asn181, Phe261, Met265, Ile262, Gln169, Lys69, Met168, Ile245, Va190, Phe242, Gln94, Val184, Asn93, Trp89, and Tyr241, for example, by polar, hydrogen bond, salt bridge, van der Waals, pi, or other interactions, as exemplified by in silico modeling of Cucurbitacin B in T2R10 (FIG. 8).

In one embodiment, the bitter taste receptor is a canine T2R43. In certain embodiments, the amino acids that the compounds interact with comprise one or more of T2R43 residues Tyr241, Trp88, and Thr181, for example, by hydrogen bonding interactions, as exemplified by in silico modeling of Propylthiouracil in T2R43 (FIG. 9). Alternatively, or in addition, in certain embodiments, the amino acids that the compounds interact with comprise one or more of T2R43 residues Met177, Asn92, Asn184, and Phe185, either alone or in conjunction with interactions listed above, for example, by polar or hydrogen bonding interactions, as exemplified by in silico modeling of Propylthiouracil in T2R43 (FIG. 9). Alternatively, or in addition, in certain embodiments, the amino acids that the compounds interact with comprise any one, two, three or more of the T2R43 residues Tyr241, Trp88, Thr181, Met177, Asn92, Asn184, Phe185, Gln152, His143, Phe261, Ala172, His85, Asp170, Lys265, Phe242, Leu245, Thr89, and Phe180, for example, by polar, hydrogen bond, salt bridge, van der Waals, pi, or other interactions, as exemplified by in silico modeling of Propylthiouracil in T2R43 (FIG. 9).

In certain embodiments, the compounds interact with any one or more of the canine T2R receptors described herein, wherein the compounds interact with one or more amino acid residues present in the 7TM domains of said receptors. The EC2 loop of said receptors is at the entrance to the active site pocket of the receptors. In certain embodiments, amino acid residues present in the EC2 loop of the bitter receptors interact with the compounds described herein.

3.3 In Vitro Methods

The presently disclosed subject matter further provides in vitro methods for identifying raw materials for generating pet food, food products, or compounds that can modulate the activity and/or expression of a bitter taste receptor.

Bitter taste receptors for use in the presently disclosed methods can include isolated or recombinant bitter taste receptors or cells expressing a bitter taste receptor, disclosed herein. In certain embodiments, the bitter taste receptor for use in the disclosed methods can comprise the amino acid sequence of any one of SEQ ID NO:17-32, or a fragment or variant thereof. In certain embodiments, the bitter taste receptor for use in the disclosed method can have at least about 33%, 34%, 35%, 40%, 45%, 50%, 55%, 60%, 61%, 65%, 70%, 72%, 75%, 79%, 80%, 84%, 85%, 87%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% identity to the amino acid sequence of any one of SEQ ID NO:17-32, or a fragment or variant thereof. In certain embodiments, the bitter taste receptor for use in the disclosed method can be encoded by a nucleotide sequence comprising any one of SEQ ID NO:1-16, or a fragment or variant thereof. In certain embodiments, the bitter taste receptor for use in the presently disclosed subject matter can include a receptor encoded by a nucleotide sequence having at least 85%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98% or at least 99% identity to any one of SEQ ID NO:1-16, or a fragment or variant thereof.

In certain embodiments, the method for identifying compounds that modulate the activity and/or expression of a bitter taste receptor comprises measuring the biological activity of a bitter taste receptor in the absence and/or presence of a test compound. In certain embodiments, the method can include measuring the biological activity of a bitter taste receptor in the presence of varying concentrations of the test compound. The method can further include identifying the test compounds that result in a modulation of the activity and/or expression of the bitter taste receptor compared to the activity and/or expression of the bitter taste receptor in the absence of the test compound.

In certain embodiments, the method can further include analyzing two or more, three or more or four or more test compounds in combination. In certain embodiments, the two or more, three or more or four or more test compounds can be from different classes of compounds, e.g., amino acids and small chemical compounds. For example, and not by way of limitation, the method can include analyzing the effect of one or more small chemical test compounds on the biological activity and/or expression of a bitter taste receptor in the presence of one or more amino acid test compounds. In certain embodiments, the method for identifying the effect of a compound on the activity and/or expression of a bitter taste receptor comprises analyzing the effect of a test compound on the biological activity and/or expression of a bitter taste receptor in the presence of a bitter taste receptor ligand, for example, a bitter tastant or bitter receptor agonist.

In certain embodiments, the method for identifying compounds that can modulate the activity and/or expression of a bitter taste receptor comprises expressing a bitter taste receptor in a cell line and measuring the biological activity of the receptor in the presence and/or absence of a test compound. The method can further comprise identifying test compounds that modulate the activity of the receptor by determining if there is a difference in receptor activation in the presence of a test compound compared to the activity of the receptor in the absence of the test compound. In certain embodiments, the method can include measuring the biological activity of the bitter taste receptor in the presence of varying concentrations of the test compound. In certain embodiments, the selectivity of the putative bitter taste receptor modulator can be evaluated by comparing its effects on other GPCRs or taste receptors, e.g., umami, fatty acid, kokumi (CaSR), T1R, etc. receptors.

In certain embodiments, the compounds identified according to the methods described herein increase or decrease the biological activity of a bitter taste receptor by at least about 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 100%, or more, compared to the biological activity of the bitter taste receptor when the compound is not present.

In certain embodiments, the method for identifying compounds that modulate the activity and/or expression of a bitter taste receptor comprises determining whether a compound modulates the receptor directly, for example, as an agonist or antagonist. In certain embodiments, the method comprises determining whether a compound indirectly modulates the activity of the receptor (e.g., as an allosteric modulator), for example, by enhancing or decreasing the effect of other compounds on activating or inhibiting receptor activity.

Activation of the receptor in the presently disclosed methods can be detected through the use of a labelling compound and/or agent. In certain embodiments, the activity of the bitter taste receptor can be determined by the detection of secondary messengers such as, but not limited to, cAMP, cGMP, IP3, DAG or calcium. In certain embodiments, the activity of the bitter taste receptor can be determined by the detection of the intracellular calcium levels. Monitoring can be by way of, but not limited to, luminescence or fluorescence detection, such as by a calcium sensitive fluorescent dye or luminescent photoprotein. In certain embodiments, monitoring can be by way of luminescence. In certain embodiments, the intracellular calcium levels can be determined using a cellular dye, e.g., a fluorescent calcium indicator such as Calcium 4. In certain embodiments, the intracellular calcium levels can be determined by measuring the level of calcium binding to a calcium-binding protein, for example, calmodulin. Alternatively and/or additionally, the activity of the bitter taste receptor can be determined by the detection of the phosphorylation, transcript levels and/or protein levels of one or more downstream protein targets of the bitter taste receptor.

The cell line used in the presently disclosed methods can include any cell type that is capable of expressing a bitter taste receptor (e.g., stable or transient expression). Non-limiting examples of cells that can be used in the disclosed methods include HeLa cells, Chinese hamster ovary cells (CHO cells), African green monkey kidney cells (COS cells), Xenopus oocytes, HEK-293 cells and murine 3T3 fibroblasts. In certain embodiments, the method can include expressing a bitter taste receptor in HEK-293 cells. In certain embodiments, the method can include expressing a bitter taste receptor in COS cells. In certain embodiments, the cells constitutively express the bitter taste receptor. In certain embodiments, the cells transiently express the bitter taste receptor. In another embodiment, expression of the bitter taste receptor by the cells is inducible.

In certain embodiments, the cell expresses a calcium-binding photoprotein, wherein the photoprotein luminesces upon binding calcium. In certain embodiments, the calcium binding photoprotein comprises the protein clytin. In certain embodiments the clytin is a recombinant clytin. In certain embodiments, the clytin comprises an isolated clytin, for example, a clytin isolated from Clytia gregarium. In certain embodiments, the calcium-binding photoprotein comprises the protein aequorin, for example, a recombinant aequorin or an isolated aequorin, such as an aequorin isolated from Aequorea victoria. In certain embodiments, the calcium-binding photoprotein comprises the protein obelin, for example, a recombinant obelin or an isolated obelin, such as an obelin isolated from Obelia longissima.

In certain embodiments, expression of a bitter taste receptor in a cell can be performed by introducing a nucleic acid encoding a bitter taste receptor into the cell. For example, and not by way of limitation, a nucleic acid having the nucleotide sequence set forth in any one of SEQ ID NO: 1-16, or a fragment thereof, can be introduced into a cell. In certain embodiments, the introduction of a nucleic acid into a cell can be carried out by any method known in the art, including but not limited to transfection, electroporation, microinjection, infection with a viral or bacteriophage vector containing the nucleic acid sequences, cell fusion, chromosome-mediated gene transfer, microcell-mediated gene transfer, spheroplast fusion, etc. Numerous techniques are known in the art for the introduction of foreign genes into cells (see, e.g., Loeffler and Behr, Meth. Enzymol. 217:599-618 (1993); Cohen et al., Meth. Enzymol. 217:618-644 (1993); Cline, Pharmac. Ther. 29:69-92 (1985), the disclosures of which are hereby incorporated by reference in their entireties) and can be used in accordance with the disclosed subject matter. In certain embodiments, the technique can provide for the stable transfer of the nucleic acid to the cell, so that the nucleic acid is expressible by the cell and inheritable and expressible by its progeny. In certain embodiments, the technique can provide for a transient transfer of the nucleic acid to the cell, so that the nucleic acid is expressible by the cell, wherein the concentration of the nucleic acid and the expression decrease in subsequent generations of the cell's progeny.

In certain embodiments, the methods can include identifying compounds that bind to a bitter taste receptor. The methods can comprise contacting a bitter taste receptor with a test compound and measuring binding between the compound and the bitter taste receptor. For example, and not by way of limitation, the methods can include providing an isolated or purified bitter taste receptor in a cell-free system, and contacting the receptor with a test compound in the cell-free system to determine if the test compound binds to the bitter taste receptor. In certain embodiments, the method can comprise contacting a bitter taste receptor expressed on the surface of a cell with a candidate compound and detecting binding of the candidate compound to the bitter taste receptor. The binding can be measured directly, e.g., by using a labeled test compound, or can be measured indirectly. In certain embodiments, the detection comprises detecting a physiological event in the cell caused by the binding of the compound to the bitter taste receptor, e.g., an increase in the intracellular calcium levels. For example, and not by way of limitation, detection can be performed by way of fluorescence detection, such as a calcium sensitive fluorescent dye, by detection of luminescence, or any other method of detection known in the art.

In other non-limiting embodiments, the in vitro assay comprises cells expressing a bitter receptor that is native to the cells. Examples of such cells expressing a native bitter receptor include, for example but not limited to, dog and/or cat taste cells (e.g., primary taste receptor cells). In certain embodiments, the dog and/or cat taste cells expressing a bitter receptor are isolated from a dog and/or cat and cultured in vitro. In certain embodiments, the taste receptor cells can be immortalized, for example, such that the cells isolated from a dog and/or cat can be propagated in culture.

In certain embodiments, expression of a bitter taste receptor in a cell can be induced through gene editing, for example, through use of the CRISPR gene editing system to incorporate a bitter taste receptor gene into the genome of a cell, or to edit or modify a bitter taste receptor gene native to the cell.

In certain embodiments, the in vitro methods of identifying a compound that binds to a T2R comprises determining whether a test compound interacts with one or more amino acids of a T2R binding pocket, as described herein.

In certain embodiments, compounds identified as modulators of a bitter taste receptor can be further tested in other analytical methods including, but not limited to, in vivo assays, to confirm or quantitate their modulating activity.

In certain embodiments, the methods of identifying a bitter taste receptor modulator can comprise comparing the effect of a test compound to a bitter taste receptor agonist or antagonist. For example, a test compound that increases or decreases the activity of the receptor in the presence of an agonist when compared to the activity of the receptor when contacted with a bitter taste receptor agonist alone can be selected as a bitter taste receptor modulating compound.

Bitter receptor agonists that can be used according to said methods can comprise one or more compounds described by Table 1.

TABLE 1 Canine Bitter Taste Receptor Agonists Compound: Chemical structure: Menthol

Ofloxacin

Chloroquine

Colchicine

1,10-phenanthroline

Cucurbitacin B

Propylthiouracil

In certain embodiments, the bitter taste receptor modulators of the present disclosure comprise a salt of the bitter taste receptor modulator, for example, but not limited to, an acetate salt or a formate salt. In certain embodiments, the bitter taste receptor modulator salt comprises an anion (−) (for example, but not limited to, Cl⁻, O²⁻, CO₃ ²⁻, HCO₃ ⁻, OH⁻, NO3−, PO₄ ³⁻, SO₄ ²⁻, CH₃COO⁻, HCOO⁻ and C₂O₄ ²⁻) bonded via an ionic bond with a cation (+) (for example, but not limited to, Al³⁺, Ca²⁺, Na⁺, K⁺, Cu²⁺, H⁺, Fe³⁺, Mg²⁺, NH₄ ⁺ and H₃O⁺). In other embodiments, the bitter taste receptor agonist salt comprises a cation (+) bonded via an ionic bond with an anion (−).

In certain embodiments, the bitter taste receptor modulators of the present application are identified through in silico modeling of a bitter taste receptor, e.g., a canine bitter taste receptor, wherein the bitter taste receptor modulators of the present application comprise a structure that fits within a binding site of the bitter taste receptor. In certain embodiments, the in silico method comprises the in silico methods described above and in the Examples section of the present application.

In certain embodiments, the bitter taste receptor modulators of the present application are identified through an in vitro method, wherein the bitter taste receptor modulator compounds modulate a bitter taste receptor, disclosed herein, expressed by cells in vitro. In certain embodiments, the in vitro method comprises the in vitro methods described above and in the Examples section of the present application.

4. Pet Food Products

The present application provides for screening methods that can be used to identify suitable raw materials to produce a palatable and nutritious pet food product. The presently disclosed screening methods can also be used to determine if a finished pet food product would be palatable to the pet (e.g., a dog). For example, the in vitro methods described herein can be used to screen raw materials and finished pet food products to identify whether the raw materials or finished pet food products comprise compounds that modulate bitter receptor activity and/or expression. In certain embodiments, raw materials and finished pet food products that do not increase the activity and/or expression of a bitter receptor can be selected for use in, or as, a pet food product for consumption. Non-limiting examples of suitable pet food products include wet food products, dry food products, moist food products, pet food supplements (e.g., vitamins), pet beverage products, snack and treats and pet food categories described herein.

One of the goals of the pet care industry is to identify sustainable protein sources for pets that do not compete with the human food chain. As such, there is an ongoing search for novel protein sources that fit these criteria. The presently disclosed screening method can be used to identify which of the novel protein sources would be considered palatable to the pet, or at least have no effect on the palatability of the other ingredients of the pet food. In certain embodiments, the novel protein source (i.e., raw material) is meat, fish, cheese, beans, yeast, yeast extracts, bacteria, algae, fungi, nuts, seeds or other plant material, or combinations thereof. In certain embodiments, the raw material is meat.

In certain embodiments, the protein source can be derived from a variety of plant sources. Non-limiting examples of plant sources include corn, maize, rice, soy, wheat, etc. For example, and not by way of limitation, the plant-derived protein can include lupin protein, wheat protein, soy protein and combinations thereof. Alternatively or additionally, the protein source can be derived from a variety of animal sources, for example, a multicellular eukaryotic organism from the kingdom animalia. Non-limiting examples of animal protein include beef, pork, poultry, lamb or fish including, for example, muscle meat, meat byproduct, meat meal or fish meal. Other non-limiting examples of animal sources include insects, or other organism from the phylum arthropoda.

In certain embodiments, the protein source can be derived from yeast or any other single-cell eukaryotic organisms, mold, mushroom or fungi.

In certain embodiments, the protein source can be derived from bacteria, archaea, or any other archaebacteria, eubacteria, or prokaryotic organism.

In certain embodiments, the protein source can be derived from algae, kelp, seaweed, or any other single or multicellular photosynthetic organism or protist.

In certain embodiments, the presently disclosed subject matter includes accepting or rejecting a raw material for the production of pet food based on the raw material's ability to enhance, increase, decrease and/or modulate the activity and/or expression of a bitter taste receptor. In certain embodiments, the raw material is rejected if the raw material results in the enhancement or increase in the activity and/or expression of at least one bitter taste receptor. In certain embodiments, the raw material is rejected if the raw material results in the enhancement or increase in the activity and/or expression of at least two, at least three, at least four, at least five, at least six, at least seven, at least eight, at least nine, at least ten, at least eleven, at least twelve, at least thirteen, at least fourteen, at least fifteen, and/or at least sixteen bitter taste receptors. In certain embodiments, the raw material is accepted if it does not modulate the activity of at least one bitter taste receptor. In certain embodiments, the raw material is selected if it inhibits or blocks the activity and/or expression of at least one bitter taste receptor. In certain embodiments, the bitter receptor is selected from any one or more of canine T2R1, T2R2, T2R3, T2R4, T2R5, T2R7, T2R10, T2R12, T2R38, T2R39, T2R40, T2R41, T2R42, T2R43, T2R62, and/or T2R67.

In certain non-limiting embodiments, a raw material that results in the enhancement or increase in the activity and/or expression of at least one bitter taste receptor can be admixed with a compound that inhibits or reduces the activity and/or expression of the at least one bitter receptor, wherein the admixture is accepted for the production of pet food.

During the production of pet food, some of the materials may change form due to mechanical forces, thermal forces, or chemical reactions. The presently disclosed screening method can be used to identify pet food products that form compounds that are unpalatable to an animal, for example, a canine, for example, a compound that enhances or increases the activity and/or expression of a bitter receptor.

In certain embodiments, the presently disclosed subject matter includes accepting or rejecting a pet food product based on the product's ability to enhance, increase, decrease and/or modulate the activity and/or expression of a bitter taste receptor. In certain embodiments, the pet food product is rejected if the product results in the enhancement or increase in the activity and/or expression of at least one bitter taste receptor. In certain embodiments, the pet food product is rejected if the product results in the enhancement or increase in the activity and/or expression of at least two, at least three, at least four, at least five, at least six, at least seven, at least eight, at least nine, at least ten, at least eleven, at least twelve, at least thirteen, at least fourteen, at least fifteen, and/or at least sixteen bitter taste receptors. In certain embodiments, the pet food product is accepted if it does not modulate the activity of at least one bitter taste receptor. In certain embodiments, the pet food product is selected if it inhibits or blocks the activity and/or expression of at least one bitter taste receptor. In certain embodiments, the bitter receptor is selected from any one or more of canine T2R1, T2R2, T2R3, T2R4, T2R5, T2R7, T2R10, T2R12, T2R38, T2R39, T2R40, T2R41, T2R42, T2R43, T2R62, and/or T2R67.

The flavor compositions of the present disclosed subject matter can also be used in a wide variety of pet food products. The combination of the flavoring composition(s) of the presently disclosed subject matter together with a pet food product and optional ingredients, when desired, provides a flavoring agent that possesses unexpected taste and imparts, for example, a desirable bitter sensory experience. The flavor compositions disclosed herein can be added prior to, during or after formulation processing or packaging of the pet food product, and the components of the flavor composition can be added sequentially or simultaneously.

In certain embodiments, the pet food product is a nutritionally complete dry, wet or semi-moist food product. A dry or low moisture-containing nutritionally-complete pet food product can comprise less than about 15% moisture. A wet or high moisture-containing nutritionally-complete pet food product can comprise greater than about 50% moisture. Such food products can include from about 10% to about 90% fat, from about 10% to about 70% protein and from about 5% to about 80% carbohydrates, e.g., dietary fiber and ash, on a percent energy basis.

In certain embodiments, the pet food product is a nutritionally complete dry, wet or semi-moist food product. In certain embodiments, the pet food product includes from about 60% fat, from about 30% protein and from about 10% carbohydrates, e.g., dietary fiber and ash, on a percent energy basis.

In certain embodiments, the pet food product is a nutritionally complete moist food product. A moist, e.g., semi-moist or semi-dry or soft dry or soft moist or intermediate or medium moisture containing nutritionally-complete pet food product comprises from about 15 to about 50% moisture.

In certain embodiments, the pet food product is a pet food snack product. Non-limiting examples of pet food snack products include snack bars, pet chews, crunchy treats, cereal bars, snacks, biscuits and sweet products.

In certain embodiments of the present disclosure, the taste and/or palatability attributes of a pet food product or medicine prepared according to the methods described herein can be measured by an in vivo tasting method that uses a panelist of taste testers. For example, but not by way of limitation, the panel can contain canine panelists. In certain embodiments, the palatability of a pet food product containing, for example, a screened raw material or a screened pet food product can be determined by the consumption of the pet food product alone (e.g., the one bowl test, monadic ranking). In certain embodiments, the palatability of a screened raw material or a screened pet food product can be determined by the preferential consumption of the pet food product or raw material, versus a pet food product that is known to be palatable to the animal (e.g., the two bowl test for testing preference, difference and/or choice).

In certain embodiments, the palatability and/or bitter blocking taste of a compound identified according to the methods described herein can be determined by the preferential consumption of a water solution containing said compound versus a water solution that does not contain the compound or contains a different flavor composition, for example, a bitter receptor agonist (e.g., the two bottle test). The intake ratio for each pet food product or water solution can be determined by measuring the amount of one ration consumed divided by the total consumption. The consumption ratio (CR) can then be calculated to compare the consumption of one ration in terms of the other ration to determine the preferential consumption of one food product or water solution over the other. Alternatively or additionally, the difference in intake (g) can be used to assess the average difference in intake between the two solutions in a two bottle test or between two pet food products in a two bowl test at a selected significance level, for example, at the 5% significance level to determine an average difference in intake with a 95% confidence interval. In certain embodiments, the confidence interval can be about 90%. However, any significance level may be used, for example, a 1, 2, 3, 4, 5, 10, 15, 20, 25 or 50% significance level.

In certain embodiments, percentage preference scores, e.g., the percentage preference for one solution or food product by an animal, is the percentage of the total liquid or food product ingested during the test that that solution or food product accounts for, can also be calculated.

5. Taste Deterrents

The present disclosure provides methods for maintaining the health of an animal by imparting a bitter taste and/or decreasing the palatability of an object or surface. In certain embodiments, the method comprises applying, coating or contacting a taste deterrent product comprising a compound identified according to the methods described herein to the object or surface, and thereby preventing ingestion of said object or surface by an animal. Accordingly, detrimental effects on the animal's health that could result from ingestion of said object or surface are avoided. In certain embodiments, the object or surface is harmful to the health of the animal or toxic to the animal.

EXAMPLES

The presently disclosed subject matter will be better understood by reference to the following Examples, which are provided as exemplary of the invention, and not by way of limitation.

Example 1—in Silico Model of Interactions Between Canine T2R Receptors and Putative Binding Compounds

The present example describes the computational modeling of canine bitter taste receptors (T2Rs) to identify putative bitter taste receptor modulators.

Homology models of canine T2R receptors were based on crystal structure of 3 SN6 from Protein Data Bank (PDB). 3 SN6 is the crystal structure of β2 adrenergic receptor from Group A GPCR with bound agonist (BI-167107 from Boehringer Ingelheim). (Rasmussen et al., Nature, 477: 549-555 (2011)). The models were built using the I-TASSER Suite of programs (Yang et al., Nat Methods, 12: 7-8 (2015)) and Modeller (Eswar et al., Curr Protoc Bioinformatics, 15: 5.6.1-5.6.30 (2006)), which is part of the DiscoveryStudio (DS) suite of programs from Accelrys (DiscoveryStudio (DS) is suite of interactive modeling and simulation programs from the Accelrys corporation).

The bitter compounds were docked into the active site of canine bitter receptors. The docking program BioDock from BioPredict, Inc., was used but other state of the art docking programs could be used for this purpose.

The results of in silico modeling are presented in FIGS. 3-9.

Example 2—Identification of Canine Bitter Receptor (T2R) Modulators Using in Vitro Assays

The present example describes an in vitro assay for identifying compounds that modulate the activation of the canine bitter taste receptor (T2R).

Compounds identified by in silico modeling with a bitter taste receptor, as detailed above in Example 1, as putative bitter taste receptor modulators will be selected for further testing in vitro. In vitro functional characterization of the selected modulators will be used to evaluate the effectiveness of a putative modulator compound in activating or inhibiting the bitter taste receptor.

HEK293 cells (or other suitable expression system) that stably or transiently express a canine bitter taste receptor (e.g., canine T2R1, T2R2, T2R3, T2R4, T2R5, T2R7, T2R10, T2R12, T2R38, T2R39, T2R40, T2R41, T2R42, T2R43, T2R62, or T2R67) will be exposed to putative compounds to modulate the activity and/or expression of the bitter taste receptor.

An exemplary method of an in vitro assay is as follows. All transient transfections will be performed with, for example, Lipofectamine2000 (Invitrogen) according to the manufactures protocol. 10 μl Lipofectamine2000 will be diluted in 500 μl DMEM (Life Technologies) and incubated for 5 minutes at room temperature. 3 μg of plasmid DNA (1 μg/μ1) will be diluted in 500 μl DMEM and added to the Lipofectamine2000 mix to obtain a final volume of 1000 μl. After additional 30 minutes of incubation at room temperature, the DNA-Lipofectamine complex will be added to 1000 μl of a cell suspension containing 1,400,000 cells/ml. Subsequently, 25 μl of the complete mixture will be seeded into each well of a black 384 well polystyrene assay plate. At 3 hours post-transfection the transfection mix will be removed from the cells and fresh DMEM containing 10% FBS and 1% P/S will be added. At 27 to 30 hours post-transfection the medium will be removed from the cells and 20 μl loading buffer that includes a calcium sensitive fluorescent or luminescent dye (Tyrode's buffer+2 μM Fluo4-AM (Invitrogen)+2.5 mM probenecid (Invitrogen) for fluorescence or Coelenterazine (Biosynth)+Tyrode's buffer for luminescence) will be added for 1 hour (fluorescence) or 3 hours (luminescence) at 37° C. The cells will then be washed 2 times every 20 minutes with Tyrode's buffer using an automated plate washer (Biochrom Asys Plate Washer) for the fluorescent protocol. No wash step will be required for the luminescent protocol.

Activation of the bitter taste receptor will then be detected, for example, by detecting a change in intracellular calcium levels using the calcium sensitive fluorescent dye, the calcium sensitive luminescent photoprotein, or by any detection system known in the art. Cells that do not express the bitter taste receptor (MOCK control) will be used as a control. Examples of such data capturing systems include FLIPR® Tetra or a FlexStation® 3 system. However, other imaging techniques and systems can be used, for example, microscopic imaging of the treated cells.

For each putative bitter taste receptor modulator, dose response curves will be generated with at least 8 concentrations in triplicate and the EC₅₀ value of the putative bitter taste receptor modulator will be determined. Graphs will be plotted, for example, in SigmaPlot V12 (Systat Software) with error bars representing standard error. The term half maximal effective concentration (EC₅₀) refers to the concentration of a compound which induces a response halfway between the baseline and the maximum after a specified exposure time.

Example 3—Identification of Canine Bitter Receptor (T2R) Modulators Using in Vitro Assays

The present example describes an in vitro assay for identifying compounds that modulate the activation of the canine bitter taste receptor (T2R) by a T2R ligand.

Compounds identified by in silico modeling with a bitter taste receptor, as detailed above in Example 1, as putative bitter taste receptor modulators will be selected for further testing in vitro. In vitro functional characterization of the selected modulators will be used to evaluate the effectiveness of a putative modulator compound in modulating the activation of the bitter taste receptor by a bitter taste receptor ligand.

HEK293 cells (or other suitable expression system) that stably or transiently express a canine bitter taste receptor (e.g., canine T2R1, T2R2, T2R3, T2R4, T2R5, T2R7, T2R10, T2R12, T2R38, T2R39, T2R40, T2R41, T2R42, T2R43, T2R62, or T2R67) will be exposed to putative modulator compounds and a bitter taste receptor ligand (e.g., an agonist) to modulate the activity and/or expression of the bitter taste receptor.

An exemplary method of an in vitro assay is as follows. All transient transfections will be performed with, for example, Lipofectamine2000 (Invitrogen) according to the manufactures protocol. 10 μl Lipofectamine2000 will be diluted in 500 μl DMEM (Life Technologies) and incubated for 5 minutes at room temperature. 3 μg of plasmid DNA (1 μg/μl) will be diluted in 500 μl DMEM and added to the Lipofectamine2000 mix to obtain a final volume of 1000 μl. After additional 30 minutes of incubation at room temperature, the DNA-Lipofectamine complex will be added to 1000 μl of a cell suspension containing 1,400,000 cells/ml. Subsequently, 25 μl of the complete mixture will be seeded into each well of a black 384 well polystyrene assay plate. At 3 hours post-transfection the transfection mix will be removed from the cells and fresh DMEM containing 10% FBS and 1% P/S will be added. At 27 to 30 hours post-transfection the medium will be removed from the cells and 20 μl loading buffer that includes a calcium sensitive fluorescent dye or luminescent substrate (Tyrode's buffer+2 μM Fluo4-AM (Invitrogen)+2.5 mM probenecid (Invitrogen) for fluorescence or Coelenterazine (Biosynth)+Tyrode's buffer for luminescence) will be added for 1 hour (fluorescence) or 3 hours (luminescence) at 37° C. The cells will then be washed 2 times every 20 minutes with Tyrode's buffer using an automated plate washer (Biochrom Asys Plate Washer) for the fluorescent protocol. No wash step will be required for the luminescent protocol.

Activation of the bitter taste receptor will then be detected, for example, by detecting a change in intracellular calcium levels using the calcium sensitive fluorescent dye, the calcium sensitive luminescent photoprotein, or by any detection system known in the art. Cells that do not express the bitter taste receptor (MOCK control) will be used as a control. Examples of such data capturing systems include FLIPR® Tetra or a FlexStation® 3 system. However, other imaging techniques and systems can be used, for example, microscopic imaging of the treated cells.

For each putative bitter taste receptor modulator, dose response curves will be generated with at least 8 concentrations in triplicate and the EC₅₀ value of the putative bitter taste receptor modulator will be determined. Graphs will be plotted, for example, in SigmaPlot V12 (Systat Software) with error bars representing standard error.

Example 4—BLAST Search Homology Comparison of Canine T2R Receptors and Human T2R Receptors

A BLAST search was conducted to compare certain canine T2R amino acid sequences with human T2R amino acid sequences. BlastP was used with parameters set as follows: Matrix Blosum 62; gap existence cost 11; gap extension cost 1; and use of compositional score matrix adjustment.

T2R2 is shared by dog and cat, but not human. A BLAST search comparison of the canine T2R2 amino acid sequence with human T2R amino acid sequences shows that the canine T2R2 was equidistant from every human T2R bitter receptor tested (Table 2).

TABLE 2 BLAST Search Homology Comparison of Canine T2R2 to Human T2R Max Total Query E Sequence Description score score Cover value Identity taste receptor type 2 172 172 93% 3e−50 35% member 7 [Homo sapiens] taste receptor type 2 158 158 97% 9e−45 33% member 9 [Homo sapiens] taste receptor type 2 143 143 97% 4e−39 32% member 10 [Homo sapiens] taste receptor type 2 141 141 97% 1e−38 33% member 8 [Homo sapiens] taste receptor type 2 134 134 93% 9e−36 31% member 41 [Homo sapiens] taste receptor type 2 133 133 97% 1e−35 29% member 13 [Homo sapiens] taste receptor type 2 129 129 95% 5e−34 32% member 1 [Homo sapiens] taste receptor type 2 129 129 97% 6e−34 34% member 42 [Homo sapiens] taste receptor type 2 120 120 96% 1e−30 29% member 39 [Homo sapiens] taste receptor type 2 117 117 97% 1e−29 31% member 5 [Homo sapiens] taste receptor type 2 115 115 91% 6e−29 30% member 60 [Homo sapiens] taste receptor type 2 115 115 93% 7e−29 32% member 43 [Homo sapiens] taste receptor type 2 115 115 96% 9e−29 32% member 30 [Homo sapiens] taste receptor type 2 113 113 96% 3e−28 31% member 45 [Homo sapiens] taste receptor type 2 112 112 96% 1e−27 30% member 40 [Homo sapiens] taste receptor type 2 111 111 95% 2e−27 32% member 3 [Homo sapiens] taste receptor type 2 109 109 95% 6e−27 28% member 16 [Homo sapiens] taste receptor type 2 107 107 92% 3e−26 33% member 31 [Homo sapiens] taste receptor type 2 104 104 96% 4e−25 30% member 46 [Homo sapiens] taste receptor type 2 102 102 94% 2e−24 28% member 19 [Homo sapiens] taste receptor type 2 102 102 95% 2e−24 28% member 38 [Homo sapiens] taste receptor type 2 100 100 76% 8e−24 31% member 50 [Homo sapiens] taste receptor type 2 100 100 96% 1e−23 29% member 20 [Homo sapiens] taste receptor type 2 99.8 99.8 94% 2e−23 29% member 4 [Homo sapiens] taste receptor type 2 99.4 99.4 94% 2e−23 28% member 14 [Homo sapiens]

T2R12 is shared by dog and cat, but not human. A BLAST search comparison of the canine T2R12 amino acid sequence with human T2R amino acid sequences shows that the canine T2R12 was equidistant from every human T2R bitter receptor tested (Table 3).

TABLE 3 BLAST Search Homology Comparison of Canine T2R12 to Human T2R Max Total Query E Sequence Description score score Cover value Identity taste receptor type 2 196 196 98% 3e−59 40% member 7 [Homo sapiens] taste receptor type 2 188 188 96% 2e−56 41% member 8 [Homo sapiens] taste receptor type 2 168 168 100%  1e−48 39% member 9 [Homo sapiens] taste receptor type 2 160 160 99% 1e−45 38% member 10 [Homo sapiens] taste receptor type 2 157 157 95% 2e−44 39% member 30 [Homo sapiens] taste receptor type 2 150 150 97% 5e−42 36% member 46 [Homo sapiens] taste receptor type 2 150 150 99% 6e−42 35% member 13 [Homo sapiens] taste receptor type 2 150 150 99% 8e−42 38% member 14 [Homo sapiens] taste receptor type 2 149 149 94% 2e−41 38% member 43 [Homo sapiens] taste receptor type 2 147 147 97% 9e−41 34% member 45 [Homo sapiens] taste receptor type 2 136 136 100%  1e−36 37% member 3 [Homo sapiens] taste receptor type 2 133 133 94% 2e−35 36% member 31 [Homo sapiens] taste receptor type 2 130 130 97% 2e−34 35% member 20 [Homo sapiens] taste receptor type 2 127 127 97% 3e−33 36% member 19 [Homo sapiens] taste receptor type 2 126 126 98% 1e−32 35% member 42 [Homo sapiens] taste receptor type 2 122 122 94% 2e−31 35% member 50 [Homo sapiens] taste receptor type 2 95.5 95.5 94% 4e−22 30% member 4 [Homo sapiens] taste receptor type 2 95.1 95.1 93% 7e−22 31% member 1 [Homo sapiens] taste receptor type 2 89.7 89.7 91% 4e−20 32% member 41 [Homo sapiens] taste receptor type 2 86.3 86.3 96% 7e−19 27% member 5 [Homo sapiens] taste receptor type 2 85.9 85.9 95% 1e−18 29% member 39 [Homo sapiens] taste receptor type 2 85.5 85.5 98% 2e−18 30% member 38 [Homo sapiens] taste receptor type 2 78.2 78.2 96% 5e−16 30% member 40 [Homo sapiens] taste receptor type 2 72.4 72.4 91% 6e−14 26% member 60 [Homo sapiens] taste receptor type 2 57.0 57.0 81% 1e−08 27% member 16 [Homo sapiens]

Canine T2R62 is unique to dog when compared to humans and felines. In particular, canine T2R62 comprises an amino acid sequence that is different from all human bitter receptors (Table 4).

TABLE 4 BLAST Search Homology Comparison of Canine T2R62 to Human T2R Max Total Query E Sequence Description score score Cover value Identity taste receptor type 2 203 203 98% 1e−62 39% member 16 [Homo sapiens] taste receptor type 2 184 184 90% 7e−55 40% member 41 [Homo sapiens] taste receptor type 2 157 157 93% 1e−44 36% member 60 [Homo sapiens] taste receptor type 2 115 115 99% 3e−29 32% member 9 [Homo sapiens] taste receptor type 2 115 115 97% 3e−29 31% member 1 [Homo sapiens] taste receptor type 2 115 115 98% 5e−29 30% member 46 [Homo sapiens] taste receptor type 2 115 115 96% 5e−29 30% member 13 [Homo sapiens] taste receptor type 2 115 115 98% 5e−29 30% member 7 [Homo sapiens]

Example 5—Identification of Canine Bitter Receptor (T2R) Modulators Using in Vitro Assays

Compounds identified by in silico modeling with a bitter taste receptor, as detailed above in Example 1, were selected for further testing in vitro. In vitro functional characterization of the selected modulators was used to evaluate the effectiveness of the putative modulator compounds in modulating the activation of the bitter taste receptors.

HEK293 cells that transiently expressed a canine bitter taste receptor selected from canine T2R1, T2R2, T2R3, T2R4, T2R5, T2R10, and T2R43, were exposed to compounds to determine whether the compounds modulated the activity of the bitter taste receptors.

All transient transfections were performed with Lipofectamine2000 (Invitrogen) according to the manufactures protocol. 10 μl Lipofectamine2000 were diluted in 500 μl DMEM (Life Technologies) and incubated for 5 minutes at room temperature. 3 μg of plasmid DNA (1 μg/μ1) was diluted in 500 μl DMEM and added to the Lipofectamine2000 mix to obtain a final volume of 1000 μl. After an additional 30 minutes of incubation at room temperature, the DNA-Lipofectamine complex was added to 1000 μl of a cell suspension containing 1,400,000 cells/ml. Subsequently, 25 μl of the complete mixture was seeded into each well of a black 384 well polystyrene assay plate. At 3 hours post-transfection the transfection mix was removed from the cells and fresh DMEM containing 10% FBS and 1% P/S was added. At 27 to 30 hours post-transfection the medium was removed from the cells and 20 μl loading buffer that included a calcium sensitive fluorescent dye or luminescent substrate (Tyrode's buffer+2 μM Fluo4-AM (Invitrogen)+2.5 mM probenecid (Invitrogen) for fluorescence or Coelenterazine (Biosynth)+Tyrode's buffer for luminescence) were added for 1 hour (fluorescence) or 3 hours (luminescence) at 37° C. The cells were then washed 2 times every 20 minutes with Tyrode's buffer using an automated plate washer (Biochrom Asys Plate Washer) for the fluorescent protocol. No wash step was required for the luminescent protocol.

Activation of the bitter taste receptor was determined by detecting a change in intracellular calcium levels as measured by fluorescence or luminescence of the calcium sensitive fluorescent dye or luminescent photoprotein. Cells that did not express the bitter taste receptor (MOCK control) were used as a control. A FLIPR® Tetra system was used to measure fluorescence or luminescence.

For each putative bitter taste receptor modulator, dose response curves were generated with at least 8 concentrations in triplicate and the EC50 value of the putative bitter taste receptor modulator was determined as shown in FIGS. 3-9. Graphs were plotted in SigmaPlot V12 (Systat Software) with error bars representing standard error.

Although the presently disclosed subject matter and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure of the presently disclosed subject matter, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the presently disclosed subject matter. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.

Patents, patent applications, publications, product descriptions and protocols are cited throughout this application the disclosures of which are incorporated herein by reference in their entireties for all purposes. 

1. A method for identifying a compound that modulates the activity of a bitter taste receptor comprising (a) contacting a test agent with a bitter taste receptor, (b) determining the activity of the bitter taste receptor, and (c) selecting as the compound, a test agent that increases or decreases the activity of the bitter taste receptor.
 2. The method of claim 1, wherein the bitter taste receptor is a canine bitter taste receptor comprising an amino acid sequence selected from the group consisting of SEQ ID NO:17-32.
 3. A method for identifying a compound that modulates the activity of a bitter taste receptor comprising (a) contacting a test agent with a bitter taste receptor, (b) detecting an interaction between the test agent and one or more amino acids of the bitter taste receptor, and (c) selecting as the compound, a test agent that interacts with one or more of the amino acids.
 4. The method of claim 3, wherein the method comprises detecting an interaction between the test agent and one or more amino acids in a 7 transmembrane domain (7TM) domain of the bitter taste receptor.
 5. The method of claim 3, further comprising determining the activity of the bitter taste receptor after step (a).
 6. The method of claim 1, further comprising contacting a bitter taste receptor ligand to the bitter taste receptor.
 7. The method of claim 1, wherein step (c) comprises selecting as the compound, a test agent that decreases the activity of the bitter taste receptor.
 8. The method of claim 1, wherein step (c) comprises selecting as the compound, a test agent that increases the activity of the bitter taste receptor.
 9. The method of claim 3, wherein the bitter taste receptor is a canine bitter taste receptor comprising an amino acid sequence selected from the group consisting of SEQ ID NO:17-32.
 10. The method of claim 9, wherein the bitter taste receptor is a canine T2R1 bitter taste receptor comprising an amino acid sequence described by SEQ ID NO:17, and wherein the one or more amino acids of the bitter taste receptor are selected from the group consisting of Asn89, Tyr239, Ile167, Gln174, Glu169, Phe257, Ala242, Phe177, His238, Cys260, Phe264, Leu234, Cys235, Phe85, Leu261, Leu178, Leu181, Va186, and Phe82.
 11. The method of claim 9, wherein the bitter taste receptor is a canine T2R2 bitter taste receptor comprising an amino acid sequence described by SEQ ID NO:18, and wherein the one or more amino acids of the bitter taste receptor are selected from the group consisting of Ser94, Trp90, Lys268, Tyr245, Glu180, Arg176, Met91, Asn185, Val184, Met181, Phe249, Pro155, Gln177, Lys174, Phe264, Phe93, Leu59, Met271, Phe246, and Leu188.
 12. The method of claim 9, wherein the bitter taste receptor is a canine T2R3 bitter taste receptor comprising an amino acid sequence described by SEQ ID NO:19, and wherein the one or more amino acids of the bitter taste receptor are selected from the group consisting of Asn93, Asp86, Tyr246, Phe247, Thr186, Asn189, Trp89, Arg175, Phe250, Gly185, Phe243, Thr90, Asn176, Val149, Ile154, Lys174, Met82, Ile85, Lys173, and Met69.
 13. The method of claim 9, wherein the bitter taste receptor is a canine T2R4 bitter taste receptor comprising an amino acid sequence described by SEQ ID NO:20, and wherein the one or more amino acids of the bitter taste receptor are selected from the group consisting of Ser186, Asp93, Tyr240, Ser94, Leu97, Asn95, Leu92, Ser96, Trp98, Val187, Thr247, Tyr243, Trp89, Met58, Ser269, Pro273, Ser270, Gln189, Thr144, Leu188, Val183, Leu182, Ser244, and Met90.
 14. The method of claim 9, wherein the bitter taste receptor is a canine T2R5 bitter taste receptor comprising an amino acid sequence described by SEQ ID NO:21, and wherein the one or more amino acids of the bitter taste receptor are selected from the group consisting of Ser89, Pro264, Leu58, Va188, Gln90, Ile86, Leu173, Trp165, Thr258, Ala261, Tyr234, Glu257, Met260, and Trp85.
 15. The method of claim 9, wherein the bitter taste receptor is a canine T2R10 bitter taste receptor comprising an amino acid sequence described by SEQ ID NO:23, and wherein the one or more amino acids of the bitter taste receptor are selected from the group consisting of Lys258, Leu180, Lys170, Glu172, Asn181, Phe261, Met265, Ile262, Gln169, Lys69, Met168, Ile245, Va190, Phe242, Gln94, Val184, Asn93, Trp89, and Tyr241.
 16. The method of claim 9, wherein the bitter taste receptor is a canine T2R43 bitter taste receptor comprising an amino acid sequence described by SEQ ID NO:30, and wherein the one or more amino acids of the bitter taste receptor are selected from the group consisting of Tyr241, Trp88, Thr181, Met177, Asn92, Asn184, Phe185, Gln152, His143, Phe261, Ala172, His85, Asp170, Lys265, Phe242, Leu245, Thr89, and Phe180.
 17. A method for identifying a compound that modulates the activity of a bitter taste receptor comprising (a) contacting a bitter taste receptor agonist with a bitter taste receptor, (b) determining the activity of the bitter taste receptor, (c) contacting a test agent with the bitter taste receptor, (d) determining the activity of the bitter taste receptor, and (e) selecting the test agent as the compound when the activity of (d) is greater or lesser than the activity of (b).
 18. A method for selecting a pet food product or component thereof, comprising (a) contacting a candidate pet food product or component thereof with a bitter taste receptor, (b) determining the activity of the bitter taste receptor, and (c) selecting as the pet food product, or component thereof, a test agent that decreases the activity of the bitter taste receptor.
 19. The method of claim 18, wherein the bitter taste receptor is a canine bitter taste receptor comprising an amino acid sequence selected from the group consisting of SEQ ID NO:17-32.
 20. The method of claim 1, wherein the bitter taste receptor is expressed by a cell, and wherein the test agent is contacted to the cell.
 21. The method of claim 20, wherein the cell expresses a calcium-binding photoprotein.
 22. The method of claim 8, further comprising contacting the compound that increases the activity of the bitter taste receptor to a surface.
 23. The method of claim 17, further comprising selecting the test agent as the compound when the activity of (d) is greater than the activity of (b), and contacting the compound that increases the activity of the bitter taste receptor to a surface.
 24. A composition comprising a compound that decreases the activity of a bitter taste receptor, wherein the compound is identified according to the method of claim
 7. 25. A composition comprising a compound that increases the activity of a bitter taste receptor, wherein the compound is identified according to the method of claim
 8. 